Mitt Romney has refused to sign a pledge opposing gay marriage, making him the first Republican presidential candidate to reject it.
The agreement, drawn up by a conservative Christian group in Iowa, calls on candidates to denounced same-sex marriage rights, pornography, same-sex military accommodations and forms of Islamic law.
Two of Romney's rivals, Michele Bachmann and Rick Santorum, have already signed The Family Leader's 14-point pledge.
Romney, who supported rights for gay couples in Massachusetts, was criticised in Iowa by some Iowa social conservatives during his 2008 campaign, when he finished second in the caucuses after aggressively courting Christian conservatives.
