The U.S. Supreme Court Wednesday hears the second of two cases that could open the door to gay marriage nationwide.
The nine justices will consider the Defense of Marriage Act, a federal law which defines marriage as being between one man and one woman.
The court heard more than an hour of arguments Tuesday on the other case -- a California law banning same-sex marriage in the state and whether that law violates the U.S. Constitution's equal protection clause.
Justice Anthony Kennedy raised concerns about whether the court was entering what he called "uncharted waters," saying the issue of same sex marriage is too new for anyone to know the sociological impact.
Recent public opinion polls show a majority of Americans now support same-sex marriage. It is legal in nine states and Washington, D.C. Supporters call it a human and civil rights issue and are hoping for a decision similar to one in 1967 that struck down state laws banning interracial marriage.
But 29 other states have passed amendments in their constitutions that outlaw gay marriage. Opponents insist the institution of marriage must be protected to ensure the family unit.