A group of church leaders and gay marriage opponents formally requested a citywide referendum yesterday to prevent Washington DC passing a law which will recognise gay marriages performed in other states.

Stand 4 Marriage DC has said it is planning to begin the process of collecting the 21,000 signatures needed to overturn the bill. The Board of Elections must first decide whether the issue should appear on the ballot.

Bishop Harry Jackson, senior pastor of Hope Christian Church in Beltsville and leader of the movement, told the Washington Post: “It’s a declaration of war. We are sending a clear message this is going to be fought every step of the way.”

If the Board of Elections allow the issue on the ballot, it could be put to voters in a special election this year or next or in next year’s council and mayoral elections.

However, gay rights activists believe it will violate the Human Rights Act and therefore be barred from appearing on the ballot.

Mark Levine, a lawyer and gay rights activist, said the elections board would be “engaged in an extraordinary act of lawlessness” if it allows the referendum to move forward.

“The DC government cannot discriminate on the basis of sexual orientation, and for them to recognise marriages of straight couples and not to recognise marriages of gay couples would be a clear violation of the Human Rights Act,” he added.

Previously, gay couples who were married in other states were recognised as domestic partners when they moved to DC but the measure means their unions will be recognised as marriages.

The bill requires that married same-sex couples must be accorded the same benefits as those received by married straight couples.