West Virginia US Senator Jay Rockefeller says he now opposes a federal law banning same-sex marriage.
However, his fellow Democrat, Senator Joe Manchin, still supports the Defense of Marriage Act.
The two West Virginia senators offered differing views as the US Supreme Court began the task of presiding over several landmark equal marriage cases on Tuesday.
It will decide the legality of same-sex marriage in the US.
Senator Rockefeller said churches and ministers should never have to perform marriages that violate their beliefs, but the federal government shouldn’t discriminate against same-sex couples.
The senator said younger West Virginians and his own children have pushed his generation to revisit its views on this issue.
As a great-grandson of oil tycoon John D Rockefeller, the 75-year-old is the currently only serving politician of the prominent six-generation Rockefeller family and the only Democrat in what has been a traditionally Republican dynasty
Meanwhile, the Associated Press reports Senator Manchin as saying that his faith has guided his belief into believing that marriage is between one man and one woman.