to the Full Faith and Credit clause:
"Second, the Full Faith and Credit Clause is not inflexible. An exception exists for those instances, such as same-sex marriage, where one state's law would contradict the public policy of another state. The United States Supreme Court has examined the Full Faith and Credit Clause on numerous occasions. In a case involving a state court's order of a money judgment, Baker v General Motors Corp, 522 US 222; 118 S Ct 657; 139 L Ed 2d 580 (1998), the Supreme Court reviewed prior decisions and noted a distinction between court judgments and a state's laws for purposes of applying the Full Faith and Credit Clause:
Our precedent differentiates the credit owed to laws (legislative measures and common law) and to judgments. . . . The Full Faith and Credit Clause does not compel "a state to substitute the statutes of other states for its own statutes dealing with a subject matter concerning which it is competent to legislate." Pacific Employers Ins Co v Industrial Accident Comm’n, 306 US 493, 501, 83 L Ed 940, 59 S Ct 629 (1939); see Phillips Petroleum Co v Shutts, 472 US 797, 818-819, 86 L Ed 2d 628, 105 S Ct 2965 (1985). Regarding judgments, however, the full faith and credit obligation is exacting. <522 US at 232-233.>
While Massachusetts now allows marriage contracts between its citizens of the same sex as a result of a state court order, the court's decision is an interpretation of Massachusetts law and not a judgment that must be given full faith and credit in other states. The United States Supreme Court offered an even clearer statement regarding the proper application of US Const, art IV, § 1, in Nevada v Hall, 440 US 410, 422; 99 S Ct 1182; 59 L Ed 2d 416 (1979), quoting Pacific Employers Ins Co v Industrial Accident Comm’n, 306 US at 502-503:
"It has often been recognized by this Court that there are some limitations upon the extent to which a state may be required by the full faith and credit clause to enforce even the judgment of another state in contravention of its own statutes or policy. . . . And in the case of statutes, the extrastate effect of which Congress has not prescribed, as it may under the constitutional provision, we think the conclusion is unavoidable that the full faith and credit clause does not require one state to substitute for its own statute, applicable to persons and events within it, the conflicting statute of another state, even though that statute is of controlling force in the courts of the state of its enactment with respect to the same persons and events."
According to the Court in Nevada v Hall, the Full Faith and Credit Clause "'does not here enable one state to legislate for the other or to project its laws across state lines so as to preclude the other from prescribing for itself the legal consequences of acts within it.'" 440 US at 423-424, quoting Pacific Employers Ins Co, 306 US at 504-505.
Michigan case law also recognizes the public policy exception to the Full Faith and Credit Clause. The Michigan Supreme Court in In re Miller's Estate, 239 Mich 455, 457; 214 NW 428 (1927), held that, were the Michigan Legislature to declare a type of out-of-state marriage to be invalid as a matter of public policy, it would be invalid in Michigan, even if valid in the state where contracted. The Legislature's declaration in MCL 551.1 that "
marriage contracted between individuals of the same sex is invalid in this state" falls squarely within this public policy exception."
http://www.ag.state.mi.us/opinion/datafiles/2000s/op10236.htm