Several Republican presidential candidates have refused to sign a marriage pledge introduced by The Family Leader, a conservative Iowa pro-family group.

Candidate Mitt Romney was the first. Now Candidates Tim Pawlenty, Jon Huntsman, Newt Gingrich and Herman Cain have also decided not to sign.

The pledge asks them to support the Defense of Marriage Act, outlaw pornography, ban gay marriage, and denounce forms of Islamic law.

"Rather than sign onto the words chosen by others, I prefer to choose my own words, especially seeking to show compassion to those who are in broken families through no fault of their own," Pawlenty said in written statement.

Pawlenty insists he would "vigorously oppose" any efforts to allow same-sex marriage.

Presidential hopefuls Michele Bachmann and Rick Santorum have already signed the pledge.

The Family Leader was formed last year and strives to have a voice in shaping Iowa's 2012 leadoff caucuses.

The group's top officials were part of a successful campaign last fall to remove three Iowa Supreme Court justices who ruled to legalize gay marriage in the state.