Republican presidential candidate Mitt Romney on Tuesday rejected a "pro-marriage" pledge created by a conservative, Iowa-based Christian group that opposes same sex marriage, Sharia law and pornography, according to the Associated Press.

A spokesperson said that while Romney "strongly supports traditional marriage," the oath "contained references and provisions that were undignified and inappropriate for a presidential campaign."

Two other GOP candidates, Michelle Bachmann and Rick Santorum, have signed the pledge.

By signing the pledge, Santorum and Bachmann vowed to remain faithful to their spouses and support a constitutional amendment banning same sex marriage, as well as agreeing that same sex marriage was akin to polygamy.

They both also promised to ban "all forms of pornography and prostitution, infanticide, abortion and other types of coercion or stolen innocence" and only appoint conservative judges.

Adding to the controversy surrounding the pledge, the original version of the document signed by Bachmann and Santorum claimed that African American children were in some respects better off under slavery than they are today.

"Slavery had a disastrous impact on African-American families, yet sadly a child born into slavery in 1860 was more likely to be raised by his mother and father in a two-parent household than was an African-American baby born after the election of the USA’s first African-American President," the document said.

The Family Leader, the Iowa-based Christian group behind the pledge, has since removed the slavery language from the vow.