(Boston, Massachusetts) Mary Ritchie, a Massachusetts State Police trooper, has been married for almost five years and has two children. But when she files her federal income tax return, she’s not allowed to check the “married filing jointly” box.

Now Ritchie, Bush and more than a dozen others are suing the federal government, claiming the act discriminates against gay couples and is unconstitutional because it denies them access to federal benefits that other married couples receive, such as pensions and health insurance. Plaintiffs also include Dean Hara, the widower of former U.S. Rep. Gerry Studds, the first openly gay member of the House of Representatives.

In Ritchie’s case, she and her spouse say they have paid nearly $15,000 more in taxes than they would have if they had been able to file joint returns.

“It saddens us because we love our country,” Ritchie said. “We are taxpayers. We live just like anyone else in our community. We do everything just like every other family, like every other married couple, and we are treated like less than that.”

The lawsuit was being filed Tuesday in federal court in Boston by Gay & Lesbian Advocates & Defenders, the anti-discrimination group that brought a successful legal challenge leading to Massachusetts becoming the first state in the nation to legalize gay marriage in 2004.

Only Massachusetts and Connecticut allow gay marriage. Vermont, Connecticut, New Jersey and New Hampshire allow civil unions.

Californians voted in November to overturn a court ruling that allowed gay marriage, but the state still offers domestic partnerships that guarantee the same rights as marriage. Hawaii is considering a bill that will allow same-sex civil unions.

The Defense of Marriage Act, or DOMA, was enacted by Congress in 1996 when it appeared Hawaii would soon legalize same-sex marriage and opponents worried that other states would be forced to recognize such marriages. The new lawsuit challenges only the portion of the law that prevents the federal government from affording Social Security and other benefits to same-sex couples.

President Barack Obama has pledged to work to repeal DOMA and reverse the Department of Defense policy that prevents openly gay people from serving in the military.

Mary Bonauto, GLAD’s Civil Rights Project director, said the lawsuit is the first major challenge to the section of the law that denies same-sex couples access to more than 1,000 federal programs and legal protections in which marriage is a factor.

All the plaintiffs are from Massachusetts and have marriages that are recognized by the state. They include a U.S. Postal Service employee who wasn’t allowed to add her spouse to her health insurance plan; a Social Security Administration retiree who was denied health insurance for his spouse; three widowers who were denied death benefits for funeral expenses; and a man who has been denied a passport bearing his married name.

“This law is an absolute intrusion into an area that states have governed for centuries – marriage,” Bonauto said.

In Hara’s case, he was denied any portion of Studds’ $114,000 pension after the Democratic congressman died in 2006. The two married in 2004 after being together for 14 years.

“I am not being treated the same as any other surviving spouse of any other federal employee or public servant who has served this country for 27 years, when I have been legally married,” Hara said.

Defendants in the lawsuit are the United States of America and several federal agencies, which are being represented by the U.S. Department of Justice.

“Obviously, we are going to take a look at it and make a determination as to how the government would ultimately respond after we review it,” DOJ spokesman Charles Miller said.

Laurence Tribe, a constitutional law professor at Harvard Law School, said the lawsuit is a “plausible challenge” to DOMA.

“It’s a question of whether Congress oversteps its bounds and engages in irrational discrimination when it draws a line in terms of concrete benefits for individuals who are otherwise eligible simply because the marriages they have entered involve same-sex couples rather than opposite-sex couples,” he said.

Opponents of same-sex marriage say those who challenge DOMA are trying to impose gay marriage on the rest of the country.

“Massachusetts has made benefits available on a state level, but Massachusetts can’t force the federal government’s hand or the other states to accept same-sex marriage,” said Mathew Staver, founder of the Liberty Counsel, a nonprofit that says it’s dedicated to advancing religious freedom and the traditional family.