Barber & Sons Tobacco, Inc., appeals a summary judgment for $169,997.80 in interest on unpaid Jackson County cigarette taxes. The Court of Appeals transferred the appeal before opinion because it involves the construction of the revenue laws of this state. Appellant contends the trial court erred because Missouri law did not authorize assessment of penalties or interest against delinquent taxpayers when this cause of action arose; subsequent legislation authorizing such an assessment cannot be applied retroactively; and a purported agreement to pay the interest assessed was not supported by consideration and therefore not enforceable as a matter of law. Reversed.
Barber & Sons is a Missouri corporation with its principal place of business in Kansas City, Jackson County, Missouri. The company is engaged in the business of selling cigarettes to retail dealers who in turn sell the cigarettes to the general public. Jackson County, Missouri, is a political subdivision of the State of Missouri, having a constitutional home rule charter. By county court order, it adopted the county cigarette tax authorized by section 210.320 RSMo.
The Director of Revenue for the State of Missouri and the Director of Revenue for Jackson County assessed Barber & Sons in the amount of $638,581.60 for Jackson County cigarette taxes which were not paid between January 1972 and May 1974; a penalty of $676,031.60 and interest of $255,-200.29 was also assessed for a total amount due of $1,569,863.59. The Department of Revenue demanded payment by March 15, 1976. The notice of assessment also informed Barber & Sons that a hearing on the matter was scheduled for March 5,1976.
Barber & Sons appeared at the hearing and objected to the notice of assessment and petitioned the Director of Revenue of the State of Missouri for reassessment. The hearing was recessed at appellant’s request in order that appellant could review its books and records. On March 30, 1976, the parties entered into negotiations to settle their dispute.
Through correspondence it was ultimately agreed that Barber & Sons would pay $638,581.60 in unpaid tax, plus an additional $169,997.80 as interest thereon. As part of this arrangement the Department of Revenue abated the original penalty and interest and agreed not to enforce criminal provisions contained in the county cigarette tax statute. On January 4, 1977, Barber & Sons petitioned the circuit court for review of the assessment under section 536.110 RSMo. The petition was dismissed with prejudice on August 23,1977, on the ground that the controversy was rendered moot by Barber & Sons’ interim payment of the principal sum of $638,581.60. The interest was never paid.
*861On February 26,1979, the Department of Revenue and Jackson County sued Barber & Sons for the amount of unpaid interest. The circuit court granted summary judgment in their favor on March 9, 1982, and ordered Barber & Sons to pay the Department of Revenue $169,997.80 plus costs.
Barber & Sons contends that section 210.-320 RSMo (1969), which was in effect during the period for which the unpaid Jackson County cigarette taxes were assessed, did not authorize the assessment of interest on such delinquent taxes and therefore it is not liable for the interest assessed on the unpaid taxes. The Department of Revenue counters this contention and argues further that Barber & Sons is liable for the unpaid interest pursuant to a valid agreement between the parties and that the attempt by Barber & Sons to avoid payment of the interest is an unlawful collateral attack on the original assessment.
I.
Jackson County’s authority to collect cigarette tax is found in section 210.320 and chapter 149 RSMo. The former statute authorizes a county cigarette tax and the latter a state cigarette tax. Section 210.320 RSMo provides that the county cigarette tax shall be collected in the same manner provided in chapter 149. Because both statutes concern the same subject matter they are in pari materia and, although found in different chapters, must be construed together. ITT Canteen Corp. v. Spradling, 526 S.W.2d 11, 16 (Mo.1975); 2A C. Sands, Sutherland Statutory Construction § 57.06 (4th ed. 1973).
Article X, Section 1 of the Missouri Constitution of 1945 provides in part that:
The taxing authority may be exercised by the general assembly for state purposes and by counties and other political subdivisions under power granted to them by the general assembly....
Hence, the power to tax is a legislative function and its exercise by a political subdivision must be based on “specific or clearly implied” authority delegated to it by the general assembly. State ex rel. Agard v. Reiderer, 448 S.W.2d 577, 579 (Mo. banc 1969). The imposition of interest on the delinquent county cigarette taxes here is an exercise of the power to tax and the specific or clearly implied authority to do so is lacking.
Section 210.320 RSMo (1969) did not provide for the assessment or collection of interest on unpaid county cigarette taxes during the period in question. Section 149.-060 RSMo (1969) did provide for a penalty equal to one hundred per cent of the amount of the tax to be assessed plus interest at the rate of six per cent per annum; however, this provision was applicable only when the taxpayer failed to affix stamps as required in that chapter. Nowhere did chapter 149 provide for an assessment of interest for a failure to pay either the state or county cigarette tax during the period in question. Under the familiar maxim of statutory construction expressio unius est exclusio alterius, the legislature in its express provision for the accrual of interest upon a failure to affix stamps, must be presumed to have intentionally negatived the accrual of interest for any other failure to comply with the statute. Maguire v. The State Savings Assoc., 62 Mo. 344, 346 (1876).
Section 210.320 RSMo was amended by the legislature in 1976 and subsection 7 thereof expressly provides that upon a failure to pay the county cigarette tax, the Director of Revenue shall assess a penalty equal to one hundred per cent of the tax due and the tax and penalty thereon shall bear interest at the rate of six per cent annum from the date such cigarettes were sold until the date of payment. Because the county cigarette taxes in this case accrued prior to the amendment, application of the statute as amended to this case would cause it to operate retrospectively in violation of article I, section 13 of the Missouri Constitution.
II.
The Department of Revenue and Jackson County contend, nevertheless, that Barber & Sons is liable for the unpaid interest in question pursuant to a valid agree*862ment between the parties. They base this argument on an exchange of letters between Barber & Sons and the Director of Revenue for the State of Missouri. Such correspondence indicates that Barber & Sons offered to pay the delinquent county cigarette taxes plus interest thereon at the rate of six per cent per annum and that the Director of Revenue purported to accept this offer. The agreement is unenforceable because of a failure of consideration on the part of the Director of Revenue.
As part of the arrangement to compromise the dispute over the amount of the unpaid county cigarette taxes, the Director of Revenue agreed not to enforce the criminal provisions of the tax statute. Consideration for a simple contract may consist of a party refraining from doing anything he has a legal right to do. Wells v. Hartford Acc. & Indem. Co., 459 S.W.2d 253, 260 (Mo.1970). If the Director of Revenue had a legal right to bring criminal proceedings against Barber & Sons, his forbearance from doing so would have been sufficient consideration to support the agreement. Respondents’ argument is deficient in that the legislature did not provide for a penalty and interest upon a failure to pay the county cigarette tax; nor did they make failure to pay such tax a crime. State v. Raccagno, 530 S.W.2d 699, 702-03 (Mo.1975). Therefore, the Director of Revenue had no legal basis on which to prosecute Barber & Sons for the failure to pay the tax and refraining from doing so was not sufficient consideration to support the agreement to pay interest thereon.
Respondents also argue that the abatement of the original penalty and interest was sufficient consideration for the agreement. It has already been demonstrated that such penalty and interest was not authorized by the statute during the period in question and respondents had no legal right to assess or collect it. Therefore, its abatement is no more a sufficient consideration for the agreement than was refraining from bringing criminal charges against Barber & Sons. See Wells, 459 S.W.2d at 260; 17 C.J.S. Contracts § 103 (1963).
Similarly, respondents argue that the compromise of the disputed claim itself was sufficient consideration for the agreement to pay interest. Such argument might have merit if this case involved the original dispute over the amount of the unpaid taxes, but the subject of the present litigation is Barber & Sons’ liability for the interest thereon. The compromise was not in settlement of the present dispute and therefore is not sufficient consideration to support the agreement to pay interest.
Respondents argue finally that Barber & Sons’ attempt to avoid the payment of interest is an unlawful collateral attack on the original assessment. There was neither specific nor clearly implied authority to collect the interest in question and the alleged agreement has been found to be unenforceable. This creates a jurisdictional defect in the assessment which renders it void and subject to collateral attack. State v. Kosovitz, 342 S.W.2d 828, 830 (Mo.1961).
Accordingly, the summary judgment in favor of respondents is reversed with direction to enter summary judgment in favor of Barber & Sons Tobacco, Inc.
WELLIVER, GUNN, BILLINGS and DONNELLY, JJ., concur. BLACKMAR, J., dissents in separate opinion filed. RENDLEN, C.J., dissents and concurs in separate dissenting opinion of BLACK-MAR, J.