Seven gay couples in the US state of New Jersey are to sue for the right to marry.
The couples, along with some of their children, say they will file a suit in the state Supreme Court today to demand that their partnerships are recognised as marriages rather than civil unions.
The move comes just a few days after neighbouring state New York legalised gay marriage.
As New Jersey governor Chris Christie has said he will refuse to sign any gay marriage bill, gay rights campaigners are taking the fight to the courts.
The couples, backed by gay groups Lambda Legal and Garden State Equality, will argue that civil unions are not good enough.
In 2006, the Supreme Court ruled that gay couples must be granted all the rights of marriage and left the legislature to decide how this should be enacted.
Lawmakers opted to legalise civil unions, but campaigners say they are not adequate because many employees in hospitals and insurance companies do not understand the concept.
One of the plaintiffs in this case says he was unable to make urgent medical decisions for his partner, while another says the health insurance of his partner and children was cancelled by an auditor who did not believe their civil union was legal.
According to the New York Times, New Jersey’s legislature apparently has enough supportive votes to pass but Governor Christie opposition is an obstacle.
He said on Sunday: “I believe marriage should be between one man and one woman.”
Earlier this month, state Senate president Stephen Sweeney said he had made the “biggest mistake” of his political career last year when he withdrew support for a gay marriage bill.
“I made a decision purely based on political calculation to not vote for marriage equality,” he said. “I failed in my responsibility as majority leader to actually lead. I was wrong.”