Rick Perry this week signed a pledge to oppose gay marriage, but a majority of the GOP presidential candidates have yet to join in.

On Friday, Perry, the current governor of Texas, joined Minnesota Rep. Michele Bachmann, former Massachusetts Governor Mitt Romney, and former Pennsylvania Senator Rick Santorum in signing the National Organization for Marriage's (NOM) promise to oppose gay marriage.

The group released a copy of the document signed by Perry on Saturday.

Candidates who sign NOM's 5-point pledge promise to support a federal constitutional amendment banning gay marriage, defend the Defense of Marriage Act (DOMA) in court, appoint judges and an attorney general who will “respect the original meaning of the Constitution,” appoint a presidential commission to investigate the “harassment of traditional marriage supporters,” and back legislation that would allow a ballot question on the issue for voters of the District of Columbia.

Perry had previously angered social conservatives by saying he was “fine” with New York's recent approval of marriage equality, because the 10th Amendment gives states the right to decide on the issue.

His new promise has prompted analysts to say Perry has retreated on federalism.

NOM cheered their victory. “Together, we are showing that support for marriage is a winning position for a presidential candidate,” NOM President Brian Brown said in a blog post.

While the race's front-runners have embraced the pledge, the majority of the GOP field, which is nearly uniformly opposed to marriage equality, has not. Fred Karger, who is openly gay, is the only candidate who supports the institution.

Two major candidates – former House Speaker Newt Gingrich and former Godfather's Pizza CEO Herman Cain – have yet to comment on the pledge.

NOM Chairwoman Maggie Gallagher recently jeered Cain for his pass.

“President Obama claimed he supported traditional marriage but then failed to follow through. If Herman Cain wants to distinguish his position from President Obama, he should commit to concrete actions, not just rhetoric in support of marriage,” she said in a blog post.