OPINION
NIX, Justice.In this appeal, the underlying facts and the chronology of events are not in dispute. The legal question raised for our consideration is whether a provision in the collective bargaining agreement between the City of Scranton (City) and the members of its Police Department is enforceable. We hold that this provision, that was voluntarily agreed to by the City during the bargaining process, cannot now be objected to by the City or its officials on the basis of its alleged illegality.
The clause in controversy was agreed upon on January 1, 1973, as part of a two-year agreement between the City and the members of its police force. The clause in controversy reads as follows:
That, the Chief of Police, and in the event the City shall employ a Commissioner of Police, or Superintendent of Police or some other similar plan, the person who fills the position must come from the ranks of the Scranton Police Department.
This clause together with the rest of the agreement was approved by the City Council and was continued in effect through calendar years 1975-76, 1977 and 1978, as part of the collective bargaining agreement and subsequent binding arbitration awards between the parties. From the clause’s adoption in 1973 until 1978, its legality was not challenged. In 1978, a newly elected mayor appointed an individual in the position of Superintendent of Police for the City of Scranton who, although well qualified for the position, did not come from the ranks of the Scranton Police Department. The collective bargaining representative for the city’s police officers, the Fraternal Order of Police (F.O.P.) instituted an action in mandamus requesting the removal of the mayor’s appointee and the appointment of a person in accordance *197with the clause in question. Subsequent to the filing of an answer, the F.O.P. filed a motion for preemptory judgment. After hearing upon the motion, the trial court issued an order dismissing the mandamus action. That action was affirmed by the Commonwealth Court.
The trial court and the Commonwealth Court focused upon whether the subject matter of the contract clause was a suitable subject for collective bargaining under the Act of June 24, 1968, P.L. 237, § 111, § 1 et seq. 43 § 217.1 et seq (Supp. 1981-82) (Act 111). The more pertinent question is whether the city or one of its officials should be allowed to raise the question at this late date.
In Pittsburgh Joint Collective Bargaining Committee v. City of Pittsburgh et al, 481 Pa. 66, 391 A.2d 1318 (1978), we held that the City of Pittsburgh could not assert the defense that a grievance arbitration procedure to which it had agreed in the bargaining process was in conflict with various provisions of the Civil Service Act, 53 P.S. § 23401 et seq. (1957 & Supp. 1978-79), such that the implementation of the procedure was prohibited by section 703 of the Public Employee Relations Act of 1970, (PERA) 43 P.S. § 1101.703 (Supp. 1978-79). In reaching this conclusion, we observed that the collective bargaining process was applied to the public sector on the premise that it would further harmonious relationships between the public employer and the employe and thereby result into a more effective and efficient operation for the taxpayer. However, to carry out that objective it was imperative that the integrity of the collective bargaining process not be undermined. In Pittsburgh, supra, we reflected that commitment to the integrity of the process by refusing to permit a city to challenge the validity of a grievance arbitration it had agreed to follow.
So too, in Ambridge Borough Water Authority v. Columbia, 458 Pa. 546, 328 A.2d 498 (1974), we refused to permit a governmental unit employer from asserting its own incapacity in an attempt to avoid arbitration, noting:
“. . . [tjhere is no question that there was a mutual agreement to arbitrate future disputes. Equally as clear *198is that there is no challenge to the capacity of the Authority to enter into an agreement providing for arbitration. Furthermore, the parties operated under this agreement for a period of three and one-half years. In this posture the lower court properly refused to reach the merits of [governmental unit employer’s] claim of lack of capacity.” Id. 458 Pa. at 551, 328 A.2d at 501.
The fact that the instant dispute does not constitute a refusal by a governmental unit to participation in an arbitration procedure it had agreed to does not provide a basis for distinction. To permit a public employer to secure an advantage in the bargaining process by agreeing to a term and subsequently avoid compliance by belatedly asserting that term’s illegality is equally inimical to the integrity of the bargaining process and undermines the harmonious relationship it was designed to foster. As noted in Pittsburgh, supra:
“To permit an employer to enter into agreements and include terms . .. which raise the expectations of those concerned, and then to subsequently refuse to abide by those provisions on the basis of its lack of capacity [or the asserted illegality of the term] would invite discord and distrust and create an atmosphere wherein a harmonious relationship would virtually be impossible to maintain.” Id. 481 Pa. at 74, 391 A.2d at 1322.
See also West Middlesex Area School District v. Pennsylvania Labor Relations Board et al, 55 Pa.Cmwlth Ct. 404, 423 A.2d 781 (1980).
It has also been previously recognized that this principle is equally applicable to the integrity of the collective bargaining process under Act 111. Grottenthaler v. Pennsylvania State Police, 488 Pa. 19, 410 A.2d 806 (1980). In Grottenthaler, quoting from Pittsburgh, supra 481 Pa. at 75, 391 A.2d 1322-23, we emphasized:
“Good faith bargaining would require that questions as to the legality of the proposed terms of a collective bargaining agreement should be resolved by the parties to the agreement at the bargaining stage.”
*199Id. 488 Pa. at 25, 410 A.2d at 809.
Act 111 specifically recognized the need for good faith bargaining as essential to the objectives it sought to obtain.
“It shall be the duty of public employers and their policemen and firemen employes to exert every reasonable effort to settle all disputes by engaging in collective bargaining in good faith...”
43 P.S. § 217.2 (Supp. 1981-82) (Emphasis added)
Obviously the statutorily mandated obligation to bargain in good faith is not met by permitting the governmental employer to avoid the performance of a term by questioning its legality after having received the advantages that flowed from the term’s acceptance.
The Commonwealth Court referred to the well recognized rule that arbitrators may not mandate that a governing body carry out an illegal act. Grottcnthaler v. Pennsylvania State Police, supra; Washington Arbitration Case 436 Pa. 168, 259 A.2d 437 (1969). However, as recognized in Grottenthaler, supra, a distinction must be drawn between situations where an arbitration panel attempts to mandate a governing body, over its objection, to carry out an illegal act and situations where the governmental unit employer attempts to belatedly avoid compliance with a term of a bargaining agreement it voluntarily agreed to during the bargaining process and thereby secure an unfair advantage in the bargaining process. See also Pittsburgh Joint Collective Bargaining Committee v. City of Pittsburgh, supra. Here, the clause in controversy was mutually agreed upon by the parties to the bargaining agreement in January of 1973 to cover a two year period. This clause, together with the remaining provisions of the agreement was presented to and approved by City Council. The legality of the provision was not raised during that stage. Thereafter the provision was continued in effect through calendar years 1975-76, 1977 and 1978, as part of the collective bargaining agreement and subsequent binding arbitration awards between the parties. Until the instant complaint was raised, the legality of the provision was not questioned. For the year *2001973, wherein the contested provision was first agreed upon, the police officers accepted a contract which did not provide for any increase in wages.1 It would be difficult to envision a more appropriate case for imposing this concept of estoppel.
Finally, we are satisfied that the application of the theory of estoppel to the instant facts does not conflict with the principle that one administration will not be permitted to bind its successor in the exercise of its discretion to make and effectuate policy. See e.g. Mitchell v. Chester Housing Authority, 389 Pa. 314, 132 A.2d 873 (1956). That principle is directed to the bad faith effort on the part of an outgoing administration to attempt to handcuff their successor. The instant facts are clearly distinguishable. The term in question was agreed upon long before the newly elected mayor’s administration was contemplated. Moreover, we are not here faced with the selection of an individual by a preceding administration, but rather a designation of the class from which that individual is to be selected. It is to be noted, there is nothing in this record that would suggest that the new administration could not obtain from this class an appointee of the competence it sought and possessing the political philosophy it desired. It also must be remembered that the provision was only binding for the year of 1978, which would have permitted the newly-elected mayor, who was entering a four-year term, to delay the selection of a new chief until the expiration of that contract. At the end of that contract period, the new administration was obviously free to decline to agree to this or any other provision it determined to be in conflict with its policy. Thus, through the bargaining process, the withdrawal of this term would be accommodated by some other concession by the governmental unit employer which would produce an agreement where each party is provided an equal opportunity to fashion *201an agreement in their best interest.2
Accordingly, the Order of the Commonwealth Court is reversed and the complaint reinstated.
McDERMOTT, J., concurs in the result. ROBERTS, J., files a dissenting opinion joined by FLAH-ERTY and HUTCHINSON, JJ.. It is reasonable to conclude that in the contracts following the 1973 agreement other considerations were received for the continuation of this term of the contract.
. It is of interest that the newly-elected mayor in 1978 has since left office and that his successor has in fact selected a chief of police in conformity with the terms of the contract provision.