Two lawsuits have been filed against the US Defence of Marriage Act, which bars federal recognition of gay marriage.

They were filed in Connecticut and New York by gay rights groups, who argue that the 1996 law, known as DOMA, violates the US constitution.

Connecticut’s lawsuit was filed by the Gay & Lesbian Advocates & Defenders on behalf of gay couples in Connecticut, Vermont and New Hampshire.

The plaintiffs are five married same-sex couples and a widower who have all been denied federal rights and protections because they are married to a person of the same sex.

In New York, the American Civil Liberties Union (ACLU) has filed a lawsuit on behalf of Edie Windsor, a widow who met her late wife Thea Spyer almost 50 years ago.

Ms Windsor was hit with a $350,000 inheritance tax bill in 2009 after Ms Spyer died. She would not have had to pay the hefty sum if the couple’s 2007 marriage in Canada had been recognised.

She said: “After Thea died, the fact that the federal government refused to recognise our marriage was devastating. In the midst of my grief at the loss of the love of my life, I had to deal with my own government saying that we weren’t a family.”

James Esseks, director of the ACLU’s LGBT Project, said: “Edie and Thea were together for 44 years, the last two of which they were lucky enough to spend as a married couple.

“Edie is seeking is the same treatment for her marriage that the federal government appropriately gives to married straight couples. It is completely unfair for the federal government to pretend that Edie and Thea were strangers, and to tax them that way.”

Mary L Bonauto, civil rights project director for Gay & Lesbian Advocates & Defenders, said: “DOMA must fall. In 1996, when Congress passed DOMA, the stated goal was to harm gay people and same-sex families with this law, and sadly, it has succeeded. Married gay and lesbian couples fall through the federal safety nets that exist for other married people.

“We have to keep the pressure on and get DOMA off the books before it does even more harm.”

In July, a federal judge in Massachusetts ruled that DOMA should be repealed. The challenge to the law was brought by state attorney-general Martha Coakley.

District Judge Joseph Tauro in Boston found that it violated states’ rights to recognise marriage as they wish, and also equality provisions in the Constitution.

President Obama called the law “abhorrent” in his 2008 election campaign but his spokeswoman said the government was obliged to defend federal laws when challenged in court.

The latest challenges seek a similar ruling and could lead to the Supreme Court looking at the issue.