One of Pennsylvania's U.S. Senators is shifting his stance on gay marriage.

Senator Bob Casey says he now supports gay marriage.

Previously the socially-conservative Democrat only supported same-sex civil unions.

Casey also says "Defense of Marriage Act" (DOMA) should be repealed.

The constitutionality of that law was argued before the Supreme Court last week.

Casey now joins several Democratic colleagues who have recently backed gay marriage.

However this isn't the first time Casey has backed gay rights.

He previously voted to allow gays and lesbians to serve openly in the military and to repeal "Don't Ask, Don't Tell."