(concurring):
I concur only in the result of the majority.
It seems to me that as enacted, Minn.Stat. § 147.01, subd. 6 (1992) is ambiguous. A statute is ambiguous if it is susceptible to more than one reasonable interpretation. Glen Paul Court Neighborhood Ass’n v. Paster, 437 N.W.2d 52, 56 (Minn.1989). Though enacted on April 29, 1992, it was not made effective until October 1, 1992. From this it is reasonable to conclude that the class of physicians whose licenses were issued or renewed between April 1 and September 30, 1992 would not be required to pay the surcharge in 1992. Instead, the first payment due would be from the class of physicians whose licenses were issued or renewed between October 1 and March 31 of 1992-93.
On the other hand, the billing for the surcharge is not required to be completed until November 15 and payment is not due until December 15. This leaves two and a half months subsequent to the statute’s effec*373tive date in which physicians whose licenses were issued or renewed before October 1, 1992 could pay the surcharge. From this it is reasonable to conclude that the legislature intended this group of physicians to pay the surcharge. Thus, I would find section 147.01, subd. 6 ambiguous.
Where the intention of the legislature is clearly manifested by plain unambiguous language, no construction is necessary or permitted. Lenz v. Coon Creek Watershed Dist, 278 Minn. 1, 9, 153 N.W.2d 209, 216 (1967). However, if a statute is ambiguous, a court may refer to the legislative history surrounding the statute’s enactment to ascertain its legislative intent. Minn.Stat. § 645.16(7) (1994).
Legislative history indicates the legislature anticipated that the annual surcharge would generate approximately $4,362 million in revenues for fiscal year 1993.1 Respondents point out that the only way the state could generate this amount of revenue for fiscal 1993 would be to surcharge both groups— approximately 11,000 physicians in all. Thus, the legislature must have intended to surcharge the group of physicians whose licenses were issued or renewed prior to October 1,1992.
Having found that section 147.01, subd. 6 applies to appellants, I would further find that it does not do so retroactively. “A retrospective law, in the legal sense, is one which takes away or impairs vested rights acquired under existing laws, or creates a new obligation and imposes a new duty, or attaches a new disability, in respect of transactions or considerations already past.” Cooper v. Watson, 290 Minn. 362, 369, 187 N.W.2d 689, 693 (1971)(quoting 50 Am.Jur., Statutes, § 476). I would read section 147.01, subd. 6(1), requiring physicians whose licenses were renewed or issued between April 1 and October 30 of 1992 to be billed for the surcharge by November 15 of 1992, as an administrative provision bearing on the order of payment of a financial obligation. In other words, that a physician’s license was issued or renewed between April 1 and September 31 of 1992 is simply an “antecedent” fact which the section draws upon for its operation. Such antecedent facts do not render a statute retroactive. Reynolds v. United States, 292 U.S. 443, 449, 54 S.Ct. 800, 803, 78 L.Ed. 1353 (1934).
Indeed, to the extent that the payment of the surcharge is associated at all with the issuance or renewal of a license, the statute provides that a license will not be renewed if the surcharge is not paid. Thus, because the 1992 licenses had already been renewed, it was the 1993 licenses that would be affected. It was made clear during oral argument that the licenses issued or renewed between April 1 and September 31, 1992 would not be affected in any way by nonpayment of the surcharge. Thus, section 147.01, subd. 6 impairs no “vested right” and does not operate retroactively.
I would also find that the statute violates no due process rights. An individual’s procedural due process rights are violated by a statute only if it divests or affects a private vested interest. Smith v. City of Owatonna, 450 N.W.2d 309, 311 (Minn.1990). As discussed above, section 147.01, subd. 6 has no effect on a physician’s current license. Rather, the statute affects renewal of a license. However, I would find an expectation in the renewal of a license not to be a vested property interest. Thus, operation of the statute would not violate due process.
Appellants also argue that the surcharge violates constitutional state and federal equal protection guarantees. Equal protection challenges to legislation which makes classifications based on social or economic criteria are examined under a rational basis standard. City of Cleburne v. Cleburne Living Ctr., 473 U.S. 432, 440, 105 S.Ct. 3249, 3254, 87 L.Ed.2d 313 (1985); see also Skeen v. State, 505 N.W.2d 299, 316 (Minn.1993). Legislative classifications will be upheld if: 1) the challenged legislation has a legitimate purpose; and 2) it was reasonable for the legislature to believe that the use of the *374challenged classification would promote that purpose. Id. Appellants do not contend the state’s interest — raising money for the general fund — is not legitimate. Rather, appellants contend no rational basis exists for dividing the physicians into two classes and then applying this statute against physicians born between April 1 and September 30. Of this argument, the court of appeals said:
The purpose of the surcharge is to generate funds to attract federal matching funds for Medicaid. The surcharge is assessed on all physicians. The division of Minnesota physicians into two groups for administrative convenience in billing is rationally related to a legitimate state interest.
Ubel v. State, No. C7-94-300, 1994 WL 284973, unpub. op. at 2 (Minn.App. June 28, 1994). I find this reasoning sound and would hold that appellants’ rights to equal protection under both the state and federal constitutions are not violated.
I would affirm the court of appeals’ holding that appellants owed the State Board of Medical Practice the $400 license surcharge on December 15, 1992 as required by section 147.01, subd. 6 (1992).
. This information is based on a document that was made available to the Senate Subconference Committee on Health and Human Services. The document entitled "Provider Specific Surcharge FY 93,” was attached to the affidavit of David Giel, a legislative analyst with the Minnesota Senate Counsel and Research Office.