Three GOP candidates say they'll support a narrowly written pledge against gay marriage.

Former Massachusetts Gov. Mitt Romney, Rep. Michelle Bachmann and former Pennsylvania Sen. Rick Santorum have all agreed to vow to the statement created by the National Organization for Marriage.

Minnesota Governor Tim Pawlenty did not agree to the marriage pledge stating they, "express their commitment to the institution of marriage using their own words in a video about their values and faith."

The NOM pledge supports a federal marriage amendment, defends the federal Defense of Marriage Act, and supports the appointment of federal judges who "will respect the original meaning of the Constitution," and oppose gay marriage.

Romney previously declined to support a more broadly written pledge against gay marriage.

That vow was created by The Family Leader -- a conservative Iowa organization -- and included controversial wording that hinted that black families were better off during slavery times.

Maggie Gallagher, chairman of the National Organization for Marriage, talked more about the importance of the marriage pledge on Newswatch, Aug. 4. Click play to watch the interview.