NEW YORK (Reuters) - Two days after same-sex marriage became legal in New York, the state's attorney general has taken legal action challenging the constitutionality of the U.S. law which defines marriage as between a man and woman.

In court papers filed on Tuesday in U.S. federal court in Manhattan, New York Attorney General Eric Schneiderman said the Defense of Marriage Act, or DOMA, violates same-sex couples' right to equal protection under the U.S. Constitution.

The 1996 law prohibits same-sex couples from receiving marriage-based benefits such as Social Security survivor benefits, health benefits and the right to file taxes jointly.

Schneiderman argued the law intrudes on the state's right to regulate marriage. On Sunday, gay couples began to marry in New York after it was made legal.

New York is the sixth and largest U.S. state to allow same-sex marriage. Connecticut, Iowa, Massachusetts, New Hampshire, Vermont and the District of Columbia also do so.

"By discriminating among married couples based on sexual orientation and sex, DOMA deprives New York of the ability to extend true equality to all marriages valid in the State," Schneiderman wrote.

Schneiderman made his arguments in support of a case brought by Edie Windsor, a woman who sued the United States last year after an inheritance from her former partner was taxed. Windsor, who was married in Canada in 2007, said she had to pay $350,000 in inheritance tax in 2009 after the federal government refused to recognize her marriage.

Windsor argued she "was forced to pay in violation of the constitutional guarantee of equal protection of the law."

In February, the Obama administration announced it would no longer defend the Defense of Marriage Act's section which defines marriage as between a man and woman.