Traditionally, marriage to a U.S. citizen enabled foreign spouses to petition for permanent legal residence in the United States. This benefit is not extended to lesbian or gay couples as immigration laws are regulated by the federal government.
Under federal law, specifically the Defense of Marriage Act (DOMA), a legal marriage is defined as a union between one man and one woman, excluding all forms of same sex marriages. This means that any rights and benefits that would normally be extended to heterosexual married couples under federal law are not afforded to couples of the same sex.
Because of this, the federal government, and thus federal immigration law, would not recognize a same sex marriage as a legal union, regardless of who performed the ceremony and where the wedding was held. As a result, the Department of Homeland Security, Citizenship and Immigration Services would not allow the foreign spouse to petition for residency on the basis of same sex marriage to a U.S. citizen.