(CNN) -- Massachusetts sued the U.S. government on Wednesday, challenging the constitutionality of a federal law that defines marriage as the union of a man and a woman.
The state of Massachusetts says the Defense of Marriage Act denies same-sex couples essential rights.
"We're taking this action today because, first, we believe that [the Defense of Marriage Act] directly interferes with Massachusetts' long-standing sovereign authority to define and regulate the marital status of its residents," Attorney General Martha Coakley said Wednesday afternoon.
"Massachusetts has a single category of married persons, and we view all married persons equally and identically," she said.
"DOMA divides that category into two distinct and unequal classes of marriage."
The lawsuit argues that the act, which became law in 1996, denies same-sex couples essential rights and protections, including federal income tax credits, employment and retirement benefits, health insurance coverage and Social Security payments.
"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 state wrote in the lawsuit, which was filed Wednesday in federal court.
Massachusetts, the first state to legalize gay marriage, said that about 16,000 same-sex couples have been married there since 2004, when it began issuing marriage licenses. Since that time, the lawsuit said, "the security and stability of families has been strengthened in important ways throughout the state. "
The state is challenging Section 3 of the law, which defines marriage as "a legal union between one man and one woman as husband and wife" and a spouse as "a person of the opposite sex who is a husband or a wife."
Before the act, the lawsuit argues, defining marital status was the prerogative of the states.
The law "eviscerated more than 200 years of federal government deference to the states with respect to defining marriage," it said.
The lawsuit also argues that the law forces Massachusetts to treat same-sex married couples differently from heterosexual married couples, particularly through determining who qualifies for the state's Medicaid program, known as MassHealth, and whether a same-sex spouse of a veteran can be buried in a veteran cemetery.
"But for DOMA, married individuals in same-sex relationships in the commonwealth would receive the same status, obligations, responsibilities, rights, and protections as married individuals in different-sex relationships under local, state, and federal laws," the lawsuit said.
The defendants named in the lawsuit include the Department of Health and Human Services, Secretary of Health and Human Services Kathleen Sebelius, the Department of Veterans Affairs, Veterans Affairs Secretary Eric Shinseki and the United States itself.
Charles Miller, a spokesman for the Department of Justice, said the department will review the case but noted that President Obama supports the legislative repeal of the Defense of Marriage Act.
In March, Gay & Lesbian Advocates & Defenders -- the same Boston-based group that successfully argued in 2003 for same-sex marriage rights in Massachusetts -- also sued the federal government over Section 3 of the Defense of Marriage Act.
Besides Massachusetts, three other states recognize same-sex marriages: Connecticut, Maine, and Iowa. Vermont and New Hampshire will join their company when same-sex marriages become legal later this year and early next year.