Rick Santorum, Mitt Romney and Newt Gingrich are being called on to repudiate a pledge from the National Organization for Marriage (NOM) each signed promising to work against gay marriage.

The GOP presidential candidates signed the group's 5-point pledge last summer.

Rival Fred Karger on Thursday called on his colleagues to drop NOM's pledge in light of recent revelations against the group, primarily that it plotted a strategy to pit minorities against gay marriage supporters.

“Mitt Romney, Rick Santorum and Newt Gingrich – you should immediately disavow the National Organization for Marriage's pledge that each of you signed,” Karger told a crowd during a speech at Towson University in Maryland. “We now have the proof that NOM is an unethical and deceitful operation.”

NOM has previous gone after Texas Rep. Ron Paul for not signing its pledge, which asks signers to support a federal constitutional amendment banning gay marriage, defend the Defense of Marriage of 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.

(Related: Antonio Villaraigosa, Vincent Gray speak out against gay marriage foe NOM's race-baiting.)