BOSTON -- Massachusetts has challenged the federal law that defines marriage as a union between a man and a woman, calling it "discriminatory and overreaching," and supporters say other states could follow suit.

The state, the first to legalize gay marriage, sued the U.S. government Wednesday over the Defense of Marriage Act. The law interferes with the right of Massachusetts to define and regulate marriage as it sees fit, Massachusetts Attorney General Martha Coakley said. The 1996 law denies federal recognition of gay marriage and gives states the right to refuse to recognize same-sex marriages performed in other states.

Massachusetts is the first state to challenge the law. Its lawsuit, filed in federal court in Boston, says the approximately 16,000 same-sex couples who have married in Massachusetts since the state began performing gay marriages in 2004 are being unfairly denied federal benefits given to heterosexual couples.

"They are entitled to equal treatment under the laws regardless of whether they are gay or straight," Coakley said at a news conference.

Besides Massachusetts, five other states -- Connecticut, Vermont, New Hampshire, Maine and Iowa -- have legalized gay marriage. Gay marriage opponents in Maine said Wednesday that they had collected enough signatures to put the state's pending law on the November ballot for a possible override.

Supporters of gay marriage predicted that other states where same-sex marriage is legal will also challenge the federal law.

"Every state has the right to determine who it will allow to marry, and the federal government always respects those decisions by states ... except in this case," said Arline Isaacson, co-chair of the Massachusetts Gay and Lesbian Political Caucus.

"(Coakley) is going right for that vulnerability in the law," she said.

The lawsuit, which argues the act "constitutes an overreaching and discriminatory federal law," focuses on the section of the law that creates a federal definition of marriage as "a legal union between one man and one woman as husband and wife."

Before the law was passed, Coakley said, the federal government recognized that defining marital status was the "exclusive prerogative of the states." Now, because of the U.S. law's definition of marriage, same-sex couples are denied access to benefits given to heterosexual married couples, including federal income tax credits, employment benefits, retirement benefits, health insurance coverage and Social Security payments, the lawsuit says.

The lawsuit also argues that the federal law requires the state to violate the constitutional rights of its citizens by treating married heterosexual couples and married same-sex couples differently when determining eligibility for Medicaid benefits and when determining whether the spouse of a veteran can be buried in a Massachusetts veterans' cemetery.

"In enacting DOMA, Congress overstepped its authority, undermined states' efforts to recognize marriages between same-sex couples, and codified an animus towards gay and lesbian people," the lawsuit states.

The defendants named in the suit include the U.S. Department of Health and Human Services, U.S. Department of Veterans Affairs and the federal government.

The Defense of Marriage Act was enacted when it appeared Hawaii would soon legalize same-sex marriages and opponents worried that other states would be forced to recognize them.

President Barack Obama has pledged to work to repeal the law, although gay rights activists criticized the administration last month after Justice Department lawyers defended it in a court brief. White House aides said they were doing their jobs to support a law that is on the books.

Charles Miller, a Justice Department spokesman, declined to comment on the lawsuit, saying the department plans to review it. He noted Obama "supports legislative repeal of the Defense of Marriage Act because it prevents (lesbian, gay, bisexual and transgender) couples from being granted equal rights and benefits."

In Maine, the Stand for Marriage Maine coalition said it took only four weeks to gather more than the 55,087 signatures necessary to put gay marriage to a vote.

The Maine law to legalize gay marriage had been scheduled to go into effect Sept. 12. It will be put on hold after the signatures are submitted and certified by the secretary of state's office. Voters will then decide in November whether the law should stand.