Adoption of hardline stance is seen as a slap in the face for the RNC leadership, which has been trying to soften party position

Social conservatives have staged a counter-offensive within the Republican party, orchestrating a unanimous vote within the party's national committee that reaffirms its opposition to gay marriage.

The counter-coup was organised at the RNC's spring meeting in Los Angeles. A resolution, passed without neither debate nor dissent from the 168 members of the party's governing committee, affirms "its support for marriage as the union of one man and one woman as the optimum environment in which to raise healthy children for the future of America".

A separate resolution that was also carried calls on the US supreme court in its pending rulings to uphold California's ban on gay marriage, Proposition 8, and to back the Defense of Marriage Act, Doma, that withholds certain federal benefits from married same-sex couples.

The adoption of such a traditionalist hardline stance by the committee is a slap in the face for the RNC's leadership, particularly its chairman, Reince Priebus, who since the drubbing received by Mitt Romney in the presidential election last November has been trying to steer the party towards a softer, more centrist position. Last month he unveiled a 100-page "Growth and Opportunity Project", dubbed the autopsy, an act of unprecedented hand-wringing over the party's failure at the polls that called for a rethinking of the party's stance on gay marriage and immigration.

"There is a generational difference within the conservative movement about issues involving the treatment and the rights of gay people – and for many younger voters, these issues are a gateway into whether the party is a place they want to be," the report said. "If our party is not welcoming and inclusive, young people and increasingly other voters will continue to tune us out."

Now the right of the Republican party is mounting a predictable backlash to that call for a shift to the centre. Earlier this week a coalition of conservative groups sent a joint letter to Priebus warning him that if he continued on the moderate path outlined in the autopsy report he risked losing the support of the party's base support.

"The Republican party makes a huge historical mistake if it intends to dismantle this coalition by marginalizing social conservatives and avoiding the issues which attract and energize them by the millions," the letter said.

The letter, coupled with the rigid response of the committee in Los Angeles, suggests that the hardline right of the party does not intend to go quietly as the leadership tries to steer it towards a more electable position. Gay conservatives reacted with dismay, warning their would be consequences.

"Today's anti-gay marriage resolution = more evidence that the GOP isn't finished losing," tweeted Jimmy LaSalvia of GOProud. "The RNC is like the alcoholic who admits he has a problem, then continues to drink."