Republican presidential candidates Ted Cruz, Ben Carson and Bobby Jindal have joined Rick Santorum in signing a promise to oppose marriage equality as president.
The National Organization for Marriage (NOM) is asking all presidential candidates to not only promise to support a constitutional amendment limiting marriage to heterosexual unions but also to "prevent the promotion of a redefined version of marriage in public schools and other government entities" and direct the Department of Justice to investigate "cases of Americans who have been harassed or threatened for exercising key civil rights to organize, to speak, to donate or to vote for marriage."
NOM President Brian Brown said in a statement that the pledge was necessary for a candidate to win his group's endorsement.
"NOM has invited every candidate for president to sign our pledge, and we encourage those who have not yet signed to do so as soon as possible," Brown said.
"We will not support a candidate for president who has not pledged to the American people to take specific actions in support of restoring marriage to our law and protecting people from government discrimination over their beliefs that marriage is the union of one man and one woman," he added.
The announcement came a day after NOM filed a report identifying the sources of the $2 million it gave to the 2009 campaign to repeal a gay marriage law approved by Maine lawmakers.
(Related: NOM reveals donors who helped repeal Maine's gay marriage law