Bachmann, R-Minn., and former U.S. Sen. Rick Santorum, R-Pa., are the only Republican candidates so far to have signed "The Marriage Vow: A Declaration of Dependence Upon Marriage and Family," The Washington Post reported. The document was written by Family Leader, a group headed by Bob Vander Plaats, a Christian evangelical and former candidate for Iowa governor.
When she put her name on the pledge Thursday, Bachmann vowed to be faithful in her marriage and to the U.S. Constitution. The document condemns homosexuality, premarital sex, Shariah law and pornography.
Bachmann entered politics as an advocate for social conservatism. But she has downplayed issues like homosexuality and abortion in interviews, saying only that she is opposed to gay marriage.
The Iowa document says there is a "complete absence of empirical proof" for the belief that homosexuality is an innate trait that cannot be changed.
On Friday, appearing on the CNBC program "Squawk Box," Bachmann said she wants to invigorate the economy as president.