The plaintiff, Lynn Teachers Union, Local 1037 (union), appeals from the judgment entered in the Superior Court affirming the decision of the Massachusetts Commission Against Discrimination (commission). The commission had upheld the decision of a hearing commissioner (commissioner); the commissioner had ruled that the union had engaged in illegal sex discrimination in violation of G. L. c. 151B, § 4 (1) (1988 ed.). The case arose out of claims by two teachers that they had been discriminated against by the school committee of Lynn (school committee) which refused to grant them preresignation credit for seniority purposes. The teachers had been forced to resign due to pregnancy.
The union challenges the judge’s decision, claiming that the original complaint filed with the commission was barred by the six-month filing limitation of G. L. c. 15IB, § 5 (1988 ed.), and that the commission’s decision that the claim was a “continuing” violation under 804 Code Mass. Regs. § 1.03(2) (1986), exempt from the statutory bar, was erroneous as matter of law. The union also argues that its bona fide, facially neutral seniority system is protected by G. L. c. 15IB, § 4 (17) (a), from claims of sex discrimination, and that the commission erred in granting the two complainants relief from the neutral application of the system. Finally, the union claims that the commission should have dismissed the original complaint because the complainants failed to make out a prima facie case of employment discrimination.
We agree with the judge’s decision that the commission’s findings of fact are supported by the evidence and that its determination that the situation presented a continuing violation was not erroneous as matter of law. We affirm. We summarize the facts as found by the hearing commissioner.1
*517Early in 1962, Joyce Angelli, a tenured teacher in the Lynn school system, learned that she was pregnant and that her child would be born around December, 1962. At that time, the rules of the school committee required that teachers who became pregnant apply for a maternity leave of absence without pay. A pregnant teacher who was granted leave had to leave employment at least four months prior to the expected date of delivery and could not return any time earlier than seven months after the birth of the child. Teachers could return from maternity leave only at the beginning of the school year, and those teachers failing to return within two years were treated as having resigned. Only tenured teachers were eligible for maternity leave; nontenured teachers who became pregnant were forced to resign.
Angelli applied for, and was granted, a maternity leave for the 1962-1963 school year. Her first child was born on December 31, 1962, and her second child was born in August, 1964. Under the rules of the school committee, Angelli could not return to work at the beginning of the 1964-1965 school year in September. Because Angelli had not returned from her maternity leave within two years, the school committee treated her as having resigned her position, effective September, 1964. Angelli took a part-time teaching position in the Lynn school system in April, 1976, returning to full-time teaching duties in September, 1977.
During the summer of 1970, Carol Griffin learned that she was pregnant and would deliver in early 1971. Griffin had been employed as a teacher in the Lynn public schools since September, 1968. Because Griffin was not a tenured teacher, she was not entitled to maternity leave and was forced to *518resign in November, 1970, due to her pregnancy. Griffin began working part time at the Lynn English High School in November, 1974, eventually returning to'a regular full-time teaching position with the Lynn school system in September, 1978.
The plaintiff union was certified in November, 1966, as the exclusive collective bargaining agent for all classroom teachers in Lynn. A collective bargaining agreement between the school committee and the union governed the terms and conditions of employment for Angelli and Griffin, both of whom were union members.2 At all times material to this case, the collective bargaining agreement provided that seniority of employees would be computed according to the number of '''‘consecutive years of experience in the Lynn School Department” (emphasis added). Because the maternity policy had forced Angelli and Griffin to leave their jobs, their total years of employment within the Lynn school system were not consecutive. Thus, the seniority system embodied in the collective bargaining agreement did not credit either Angelli or Griffin for those years of employment preceding pregnancy and subsequent resignation.
In June, 1980, Griffin began to inquire about obtaining seniority credit for her preresignation employment. Her efforts at that time were unsuccessful. In November, 1980, the Massachusetts electorate voted to implement Proposition 2xh. St. 1980, c. 580. Anticipating a layoff of teaching personnel due to Proposition 2lh, the union requested that the school committee delineate each teacher’s seniority.
On March 4, 1981, both Angelli and Griffin (complainants) filed a “charge of discrimination” with the commission against the school committee for its failure to credit the complainants for their service prior to the forced resignations. It was not until March 18, 1981, when the school committee distributed the seniority list which the union had requested, *519that the complainants formally learned that the committee would not credit their prior service.3
In August, 1982, the school committee voted to grant Griffin and Angelli seniority credit for their preresignation service. The union, however, grieved the committee’s decision as a violation of the collective bargaining agreement. An arbitrator upheld the grievance, and, as a result, both teachers were sent a termination notice. Griffin and Angelli filed amended complaints in November, 1982, naming the union as well as the school committee as respondents.
On February 21, 1985, the hearing commissioner issued her decision finding that the union had discriminated against the complainants on the basis of their sex in violation of G. L. c. 151B, § 4.4 The union was ordered to credit the complainants for their preresignation seniority and to pay Griffin $1,000 plus interest to compensate for her emotional distress. The union appealed the decision to the full commission which upheld the hearing commissioner’s decision on September 25, 1985. Pursuant to G. L. c. 30A, § 14 (1), the union applied for judicial review of the commission’s decision. On July 5, 1988, a judge of the Superior Court affirmed the decision of the commission. The union appealed the decision of the Superior Court. *5201. G. L. c. 151B, § 4 (1), and the application of the continuing violation rule. General Laws c. 151B, § 4 (1), prohibits discrimination in the “terms, conditions or privileges of employment” on the basis of an employee’s sex.5 Any person who feels that his or her rights under G. L. c. 15IB, § 4. (1), have been violated may file a complaint with the commission, which has the power to hold hearings and render judgments regarding claims of unlawful discrimination. G. L. c. 151B, § 3 (1) - (13). Ordinarily, a complaint of unlawful discrimination must be filed with the commission within six months of the alleged act of discrimination. G. L. c. 15IB, § 5. However, this six-month limitation will not be applied where “the unlawful conduct complained of is of a continuing nature.” 804 Code Mass. Regs. § 1.03(2). Where there is a determination of a continuing violation, a complaint is timely filed even though the discriminatory action commenced more than six months prior to the challenge. See Rock v. Massachusetts Comm’n Against Discrimination, 384 Mass. 198, 207-208 (1981). The purpose of this “continuing violation” rule is to permit the commission to “remedy ongoing discriminatory policies by an employer.” Id. at 207.
In the present case, the commission decided that the union’s failure to credit the complainants for their preresignation seniority was a continuing violation, thereby releasing the complainants from the six-month filing limitation of G. L. c. 151B, § 5. The union challenges this decision, claiming that the only discriminatory acts occurred in 1964 and 1970, when the maternity leave policy dictated the resignation of the complainants.6 Such acts, the union argues, are *521too remote to meet the filing requirements of G. L. c. 15IB, § 4.
The commission found a continuing violation of G. L. c. 151B, § 4 (1), in the failure of the union to credit the complainants with their preresignation seniority under the seniority system’s requirement of consecutive years of service. The commission reasoned that, because the number of the complainants’ consecutive years of service had been reduced by an illegal maternity leave policy, the seniority system gave effect to that discriminatory policy by failing to credit the complainants for their preresignation service. According to the commission, the complainants underwent a new act of illegal discrimination each day that their status on the seniority list remained lower than it would have been but for the illegal maternity leave policy. Thus, under this analysis, the union’s refusal to credit the complainants with their preresignation seniority was a daily, continuing violation of G. L. c. 15IB, § 4 (1).
The union claims that the application of a facially neutral seniority system cannot be considered a discriminatory act for the purposes of the continuing violation rule, even though it gives present effect to a past act of discrimination. The union points to the decision in United Air Lines, Inc. v. Evans, 431 U.S. 553 (1977), in support of its contention.7 We find its arguments unpersuasive.
*522While the union is correct in pointing out that the seniority system is facially neutral and does not explicitly adopt the discriminatory rule contained within the original maternity leave policy, the union ignores the fact that the seniority system credits the complainants with fewer years of employment than they have served solely because they became pregnant during their employment and were forced to resign.
The union argues that the seniority system does not treat the complainants any differently than “any other employee, male or female, who returned to teaching after several years absence, whether the initial separation was voluntary or involuntary." But the union has failed to consider the more telling issue whether the seniority system discerns between “initial separations” which are legal and those which are illegal. We are not concerned with the seniority system’s responsiveness to the desires of those teachers who leave their jobs voluntarily; rather, we are concerned with the seniority system’s responsiveness to the rights of those teachers who are forced to leave. A seniority system which is so “facially neutral” that it ignores prior discriminatory acts against its members, to the detriment of those members, presents a ready vehicle for application of the continuing violation rule.
In Rock v. Massachusetts Comm’n Against Discrimination, 384 Mass. 198, 207 (1981), we described the purpose of the continuing violation rule as “[permitting the commission] to remedy ongoing discriminatory policies.” In the present case, that purpose is met by the commission’s application of the continuing violation rule. The union’s refusal to credit the complainants’ preresignation seniority springs directly *523from the discriminatory maternity leave policy. Had the union been willing to alter its seniority system to disregard breaks in service caused by illegal acts, the effects of the maternity leave policy would have gradually disappeared. Instead, the union’s refusal to credit the complainants for their preresignation seniority breathes new life into a concededly illegal policy. Given the union’s knowledge that the complainants were illegally forced to resign, the refusal to credit the complainants constituted a discriminatory act in violation of G. L. c. 15IB, § 4. We agree with the Court of Appeals of New York, which, on similar facts, concluded that a continuing violation existed and stated that such a seniority system “imposes a distinct burden on a woman who became pregnant during service, effectively penalizing her again for her prior pregnancy” (emphasis added). Board of Educ. of Farmingdale Union School Dist. v. State Div. of Human Rights, 56 N.Y.2d 257, 261-262 (1982).
The commission has been charged with the task of combating discrimination in the Commonwealth and, pursuant to its statutory powers, has developed the continuing violation rule to assist in carrying out its legislative mandate. To limit the continuing violation rule to the interpretation proposed by the union would be to strip the rule of its vitality, while allowing the dead hand of past discrimination to reach out to revisit illegal discrimination upon its past victims again and anew. To this we cannot agree.
2. The seniority system and application of G. L. c. 151B, § 4 (17) (a). General Laws c. 151B, § 4 (17) (a), provides: “Notwithstanding any provision of this chapter, it shall not be an unlawful employment practice for any person, employer, labor organization or employment agency to: . . . observe the terms of a bona fide seniority system . . . which is not a subterfuge to evade the purposes of this section, except that no such seniority system . . . shall require or permit the involuntary retirement of any person because of age except as permitted by paragraph (6)” (emphasis supplied). The union claims that G. L. c. 151B, § 4 (17) (a), releases its bona fide seniority system from the requirements of *524G. L. c. 15IB, § 4, and that the commission erred in deciding that the statutory exemption did not apply to cases of sexual discrimination.
The union presented this same argument to both the commissioner and the commission, and in each instance it was rejected. As we review the validity of the commission’s decision, we keep in mind that “[a]n agency’s interpretation of a statute, under which it is vested with broad authority to effectuate the purposes thereof, is entitled to great weight.” Polednak v. Rent Control Board of Cambridge, 397 Mass. 854, 858 (1986). Therefore, the commission’s determination that the statutory exemption did not apply in the present situation is not to be disregarded lightly.
The commissioner noted that § 4 (17) (a) was inserted in G. L. c. 15IB, § 4, by St. 1984, c. 266. Chapter 266 is entitled, “An Act relative to the dismissal of certain persons from employment or the refusal to employ such persons due to age.” Chapter 266 consists of seven sections, each of which amends various chapters of the General Laws regarding their treatment of “age” in the employment context.
This court has recognized that, “[wjhile the title to an act cannot control the provisions of the statute, the title may be used for the purpose of ascertaining its proper limitations.” Commonwealth v. Graham, 388 Mass. 115, 120 (1983). American Family Life Assurance Co. v. Commissioner of Ins., 388 Mass. 468, 474 (1983). Similarly, we have held that, in interpreting a statute this court may consider “the cause of [the statute’s] enactment, the mischief or imperfection to be remedied and the main object to be accomplished.” O’Brien v. Director of the Div. of Employment Sec., 393 Mass. 482, 488 (1984), quoting Industrial Fin. Corp. v. State Tax Comm’n, 367 Mass. 360, 364 (1975).
The title and provisions of c. 266 make clear the intent of the Legislature to focus exclusively on the problem of age discrimination in the workplace. General Laws c. 15IB addresses issues of discrimination on the basis of race, color, religious creed, national origin, age, sex, or ancestry. However, c. 266 refers explicitly only to age discrimination in its *525amendment to c. 151B, to the exclusion of all other forms of discrimination encompassed by c. 15IB. Had the Legislature intended to affect the statutory treatment of other forms of discrimination, it would have made some reference to these other types of discrimination in either the title or the provisions of c. 266. Brady v. Brady, 380 Mass. 480 (1980).8
We agree with the commissioner that, by its addition of paragraph (17) (a) to G. L. c. 15IB, § 4, the Legislature did not intend to screen bona fide seniority systems from the scrutiny of all of the Commonwealth’s antidiscrimination laws. Because the present case involves a case of discrimination on the basis of sex, the provisions of G. L. c. 151B, § 4 (17) (a), do not apply.9
*5263. Prima facie case of employment discrimination. The union claims that the complainants failed to establish a prima facie case of employment discrimination, and therefore the commission erred in not dismissing the complaints. We disagree. When an employment act or practice is challenged as discriminatory, the burden of proof as to the unlawfulness of the act or practice falls on the challenging party. Sarni Original Dry Cleaners, Inc. v. Cooke, 388 Mass. 611, 614-615 (1983). “[P]roof of a prima facie case establishes that, in the absence of other and lawful explanation, the challenged employment decision was based on impermissible and discriminatory factors in violation of G. L. c. 15IB.” Id. at 615.
A prima facie case of employment discrimination can be based on a theory of disparate impact or disparate treatment.10 School Comm. of Braintree v. Massachusetts Comm’n Against Discrimination, ill Mass. 424, 428 (1979). The complainants chose to present the matter to the hearing commissioner as one of disparate treatment. A prima facie case of disparate treatment requires that the challenging party make a showing that he or she was discriminated against in employment on the basis of illegal considerations. Id. In addition, the challenging party must prove discriminatory intent or motive. Smith College v. Massachusetts Comm’n Against Discrimination, 376 Mass. 221, 227 (1978).
*527In the present case, complainants made a showing that the seniority system in question placed a unique burden on female employees who were unlawfully forced to resign due to their pregnancies. The hearing commissioner agreed with the complainants that the seniority system discriminated against the complainants because of their sex in violation of G. L. c. 151B, § 4 (1). This presented the commission with a showing sufficient to meet the prima facie requirement of discrimination based on illegal considerations. The prima facie requirement of proof of intent may be met by a “showing] that the employer’s actions were deliberate, rather than accidental.” Sami Original Dry Cleaners, Inc. v. Cooke, 388 Mass. 611, 616 (1983). In addition, discriminatory intent “may be inferred from the mere fact of differences in treatment.” School Comm. of Braintree v. Massachusetts Comm’n Against Discrimination, supra at 429. The commission had before it the findings of the hearing commissioner which made clear the fact that the union was well aware that the seniority system denied the complainants their preresignation seniority because they had been forced illegally to resign. In light of this evidence, we cannot say that the commission erred as matter of law in failing to dismiss the complaints for lack of a prima facie case.
Based on our review of the entire record, we discern no error of law in the commission’s decision; we conclude that the decision is supported by substantial evidence. Accordingly, the judgment of the Superior Court affirming the decision of the commission contains no error.
Judgment affirmed.
Upon appeal, the full commission is required to review the record which was before the hearing commissioner. G. L. c. 151, § 3 (1988 ed.). According to the commission’s rules of procedure, the commission should accept the facts found by the hearing commissioner unless they are “[u]nsupported by substantial evidence.” 804 Code Mass. Regs. § 1.16(8) *517(1986). Similarly, G. L. c. 30A, § 14 (7) (e) (1988 ed.), requires that a court reviewing a decision of the commission accept the factual findings of the commission unless they are “ [unsupported by substantial evidence.” New York & Mass. Motor Serv., Inc. v. Massachusetts Comm’n Against Discrimination, 401 Mass. 566 (1988). Sarni Original Dry Cleaners, Inc. v. Cooke, 388 Mass. 611 (1983). “Substantial evidence” has been defined as “such evidence as a reasonable mind might accept as adequate to support a conclusion.” G. L. c. 30A, § 1 (6) (1988 ed.). Katz v. Massachusetts Comm’n Against Discrimination, 365 Mass. 357 (1974).
The collective bargaining agreement between the school committee and the union at the time of Griffin’s pregnancy incorporated the same maternity leave policy which had mandated Angelli’s resignation in 1964 and Griffin’s resignation in 1970.
The union claims that the commission’s findings that Angelli and Griffin did not formally learn of their seniority status until March 18, 1981, is not supported by substantial evidence. The union points to the filing of the discrimination charges on March 4, 1981, and the testimony of both Angelli and Griffin that they knew they were treated as “new” employees when they returned to work in the Lynn school system. The hearing commissioner specifically rejected the union’s claim, characterizing the evidence offered by the union as indicating uncertainty on the part of the complainants as to their seniority status and citing her observation of the witnesses’ demeanor during testimony. Under the standards of review outlined in note 1, supra, we decline to overturn the hearing commissioner’s finding. See CollegeTown, Div. of Interco, Inc. v. Massachusetts Comm'n Against Discrimination, 400 Mass. 156, 170 (1987).
The hearing commissioner also ruled that the school committee had discriminated against the complainants. The school committee did not appeal this decision to the full commission. Therefore, the present case before this court involves only the union’s appeal from the commissioner’s decision.
General Laws c. 151B, § 4 (1), provides: “It shall be an unlawful practice: 1. For an employer, by himself or his agent, because of the race, color, religious creed, national origin, sex or ancestry of any individual, to refuse to hire or employ or to bar or to discharge from employment such individual or to discriminate against such individual in compensation or in terms, conditions or privileges of employment, unless based upon a bona fide occupational qualification.”
The union properly has conceded that the maternity leave policy responsible for the complainants’ resignations was illegal. This court declared a similar policy unconstitutional under the due process clause of the *521Fourteenth Amendment to the United States Constitution in Black v. School Comm, of Malden, 365 Mass. 197 (1974). In Black, this court declared that such a restrictive policy “ ‘[penalizes a] pregnant teacher for deciding to bear a child,’ [thereby putting] a heavy burden on the ‘freedom of personal choice in matters of marriage and family life [that] is one of the liberties protected by the Due Process Clause.’ ” Id. at 206, quoting Cleveland Bd. of Educ. v. LaFleur, 414 U.S. 632, 639-640 (1974). It is clear that such a policy violates G. L. c. 151B, § 4 (1). See 804 Code Mass. Regs. § 8.01(3). See also School Comm. of Braintree v. Massachusetts Comm’n Against Discrimination, 377 Mass. 424 (1979) (sick leave policy denying benefits to pregnancy-related disabilities violative of G. L. c. 15IB, § 4, as unlawful discrimination).
Evans considered a charge of a continuing violation brought under Title VII of the Civil Rights Act of 1964, involving the allegedly discriminatory application of a seniority system to an employee who had been forced to *522resign because of her marriage. United Airlines, Inc. v. Evans, 431 U.S. 553 (1977). While this court may consider analogous Federal statutes for purposes of interpretation, we “are not . . . bound by interpretations of the Federal statute in construing our own State statute.” College-Town, Div. of Interco, Inc. v. Massachusetts Comm’n Against Discrimination, 400 Mass. 156, 163 (1987). Massachusetts Elec. Co. v. Massachusetts Comm’n Against Discrimination, 375 Mass. 160, 167 (1978). Because we view the Evans decision as unduly restrictive of an administrative-agencyls ability to punish discriminatory acts, for the reasons stated infra, we decline to follow its reasoning regarding continuing violations. .
By comparison, the language of § 703(h) of Title VII, 42 U.S.C. § 2000e-2h (1982), which has been held to provide an exemption for bona fide seniority systems from the application of Federal laws prohibiting varied types of discrimination, specifically refers to “an intention to discriminate because of race, color, religion, sex, or national origin. “
The dissent points to our “[refusal] to follow Federal precedents construing parallel provisions of Federal law,” and argues that we should adopt the interpretation ascribed by Federal courts to language in Title VII similar to that in § 4 (17). However, this argument fails to recognize that “Title VII and the decisions construing it are not determinative of the questions presented in this case; rather the issue presented is purely one of the interpretation of a Massachusetts statute.” Massachusetts Elec. Co. v. Massachusetts Comm'n Against Discrimination, supra at 167. Even if we were to look to the Federal system for guidance, we would encounter conflicting signals. While § 4 (17) is similar to § 703(h) of Title VII, c. 14, § 623(f)(2) of Title XXIX contains language virtually identical to that used in § 4 (17) (a). 29 U.S.C. § 623(f)(2). Congress passed c. 14 for the sole and specific purpose of addressing age discrimination in employment. 29 U.S.C. § 621(b). Therefore, it is unclear whether we should look to Title VII or Title XXIX for illumination. We choose to look to neither.
The dissent also states that our interpretation of § 4 (17) will render the seniority system exemption “practically meaningless.” This conclusion rests upon the rather dubious assumption that seniority systems, by their very nature, protect older workers and therefore do not need protection from age discrimination claims. The dissent fails to recognize the realities of the modern workplace, in which it is quite common for workers to enter new jobs in the latter stages of their lives. See Carey, Occupational Tenure in 1987, Monthly Labor Review 4 (Oct. 1988) (10.5% of workers aged fifty to fifty-four have tenure of less than six to nine years). These older workers will receive less protection from a seniority system than is anticipated by the dissent, and will owe less allegiance to the system. The Legis*526lature recognized that length of seniority does not necessarily equate with chronological age, and that older workers will not always receive better treatment under a seniority system. Section 4 (17) is a reflection of that recognition, and is designed to protect seniority systems from the appearance of age discrimination inherent in a situation where a younger worker receives benefits at the expense of an older worker.
“[Disparate impact] cases involve employment practices that are facially neutral in their treatment of different groups, but that in fact fall more harshly on one group than another.” School Comm. of Braintree v. Massachusetts Comm’n Against Discrimination, ill Mass. 424, 429 (1979). Disparate treatment cases generally involve situations where an employer “purposefully uses race, color, religion, sex, or national origin as the determinative factor in employment decisions.” Id. at 428.