Gay equality opponents in Washington DC were barred by a judge from holding a referendum on gay marriage yesterday.
Same-sex marriage is expected to become legal in March so long as a Congressional review approves it.
Although 31 US states have held referendums on gay marriage, Judge Judith N Macaluso threw out a lawsuit from gay marriage opponents arguing for a voter decision.
Macasulo wrote: “If enacted, the initiative would deprive only same-sex individuals of the legal status, rights, and privileges they enjoy as married persons.”
She added it would “authorise discrimination” and violate human rights laws.
A group of Republican Congress members had signed the lawsuit and are expected to appeal the decision.
Gay marriage is currently legal in five states but has never been granted by voters. Instead, marriage equality rights have always been granted by courts or legislature.
Voters in California repealed a gay marriage law in 2008, while Maine voters prevented a similar law being enacted in the autumn.
The gay marriage bill in DC was signed by mayor Adrian Fenty last month.
The district will follow Massachusetts, Vermont, Iowa, New Hampshire and Connecticut in allowing gay couples to marry.