This didn't take long:

The New York State attorney general, Eric T. Schneiderman, acting just days after the state began allowing gay couples to wed, filed a legal brief on Tuesday challenging the constitutionality of the federal Defense of Marriage Act.

Mr. Schneiderman asserted that the law, which prohibits the federal government from recognizing same-sex marriages, violates the right to equal protection under the law for gay and lesbian couples.

The brief (attached at the bottom of the post), filed in Federal District Court in the Southern District of New York, refers specifically to New York State’s Marriage Equality Act, which was approved by lawmakers last month and took effect to great fanfare on Sunday. --NYTimes' City Room blog