The decision came a day after a federal judge ruled that Louisiana's law limiting marriage to heterosexuals is constitutional. The ruling was the first in federal court upholding a ban on gay marriage since the U.S. Supreme Court overturned the Defense of Marriage Act last year.
The 7th Circuit Court of Appeals in Chicago, on the other hand, upheld lower court rulings that Wisconsin and Indiana must allow same-sex couples to wed.
"More than unsupported conjecture that same-sex marriage will harm heterosexual marriage or children or any other valid and important interest of a state is necessary to justify discrimination on the basis of sexual orientation.As we have been at pains to explain, the grounds advanced by Indiana and Wisconsin for their discriminatory policies are not only conjectural; they are totally implausible," Judge Richard Posner wrote for the unanimous court.
Dana Brueck, a spokeswoman for Wisconsin Attorney General J.B. Van Hollen, said the Supreme Court will have the last word. Van Hollen and Gov. Scott Walker, both Republicans, are opponents of gay marriage.
Views on gay marriage across the country have shifted since 2004 when the Massachusetts Supreme Judicial Court ordered that state to allow same-sex marriage. In 2006, 59 percent of Wisconsin voters supported a constitutional amendment banning gay marriage, but a Marquette University Law School poll showed 56 percent would now vote the other way.