Though GOP presidential candidate Mitt Romney has caught flack for apparent flip-flops on abortion issues, perhaps none are quite as critical of him as “fetal personhood” supporters. The “personhood” movement wants governments to legally define a human being from the moment of conception, and Keith Mason, the head of Personhood USA, is saying that Romney should clarify his stance on the issue.

The “Personhood” movement is controversial because of its vague nature. Defining a human being from the moment of conception, as some critics have pointed out, could have a host of unintended consequences for some — like birth control users and those hoping to undergo in vitro fertilization procedures.

Though he has supported abortion in the past, Romney appeared to endorse ”Personhood” during an interview with Mike Huckabee, saying he would “absolutely” support a constitutional amendment that would establish the definition of life at conception. It’s worth noting that Romney appeared flustered after giving that answer and later said he “probably would” support the measure.

But comments he made during a Labor Day forum in South Carolina rubbed many anti-abortion advocates the wrong way. When asked whether he supported the use of the Fourth Amendment to overturn Roe v. Wade, Romney said that he did not, for fear that it would lead to a “constitutional crisis” among the branches of government.

“I strongly disagree in that the Supreme Court is actually the one that created the crisis with Roe vs. Wade,” said Mason, in response. “But I think it showcases the simple fact that Roe vs. Wade is not the end-all and be-all of being successful with ending abortion in America. … Personhood is in the heart of Roe vs. Wade, and they understood that if we acknowledge that the pre-born child is a person, that the argument for abortion collapses.”

Now Mason says he has grown tired of Romney’s seeming unwillingness to pick a side — and Mason says a position on Mississippi’s Amendment 26 would be a “good step forward.”

Via Politico:

“We always seem to get two stories from Romney,” said Keith Mason, co-founder of a group supporting the Mississippi’s initiative, Personhood USA. “If he comes out with a position for Amendment 26 in Mississippi, that would be a good step forward.”

The Mississippi measure would add a single line to the state constitution: “The term ‘person’ or ‘persons’ shall include every human being from the moment of fertilization, cloning or the functional equivalent thereof.”

Romney’s campaign did not respond to requests for comment. But Romney has stated, “I am pro-life and believe that abortion should be limited to only instances of rape, incest or to save the life of the mother.” He also thinks Roe should be overturned.