(CNN) -- Mississippi Gov. Haley Barbour offered his support Friday for an amendment to the state constitution that would define life as beginning at the moment of conception, saying he cast his absentee ballot for the measure despite struggling with its implications.

"I have some concerns about it," he said in a statement issued Friday, a day after casting his ballot. "But I think all in all, I believe life begins at conception, so I think the right thing to do was to vote for it."

On Wednesday, Barbour, a Republican, said that he was still undecided and that the measure was "too ambiguous."

Initiative 26 would define personhood as "every human being from the moment of fertilization, cloning or the functional equivalent thereof."

Though the text of the amendment is simple, the implications if it passes couldn't be more complex. If approved by Mississippi voters on Tuesday, it would make it impossible to get an abortion and hamper the ability to get some forms of birth control.

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Because the amendment would define a fertilized egg as a person with full legal rights, it could have an impact on a woman's ability to get the morning-after pill or birth control pills that destroy fertilized eggs, and it could make in vitro fertilization treatments more difficult because it could become illegal to dispose of unused fertilized eggs. This could lead to a nationwide debate about women's rights and abortion while setting up a possible challenge to the landmark Roe v. Wade case, which makes abortion legal.

The ballot initiative is part of a national campaign brought by Personhood USA. The Colorado-based group describes itself as a nonprofit Christian ministry that "serves the pro-life community by assisting local groups to initiate citizen, legislative, and political action focusing on the ultimate goal of the pro-life movement: personhood rights for all innocent humans."

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The idea for personhood was born during Roe v. Wade's oral arguments, when Justice Potter Stewart said, "If it were established that an unborn fetus is a person, you would have an impossible case here." Now, Personhood USA is trying to use the amendment to establish "personhood" as a direct challenge to the Roe v. Wade ruling.

The initiative has been gaining support across many demographics, according to polls suggesting that it will probably pass.

The Mississippi State Medical Association and Doctors Against MS 26 are voicing concern about implications for the health care of women as well as their ability to practice medicine.

Clergy and church officials in the heavily religious state are split on the issue. Some anti-abortion religious groups say they think this step may be so extreme, it could lead to a Supreme Court ruling that actually strengthens Roe v. Wade.

The Democratic and Republican candidates for governor have both said they are behind the amendment, and Attorney General Jim Hood, a Democrat, has said he would enforce the measure if it passed.

While Barbour said he still has concerns, he said in a statement Friday that a group opposed to the measure is calling Mississippi voters and telling them he is opposed to it.

"These misleading calls were made without my knowledge, without my permission and against my wishes," Barbour's statement said. "I have demanded that this deception be stopped, and those responsible have assured me that no more calls will be made."

The governor's office identified the group as Mississippians for Healthy Families.

A statement from the group said the calls used "the exact words of Gov. Haley Barbour about the 'unintended consequences' caused by this dangerous initiative," noting that the concerns expressed earlier in the week by the governor "echo those of doctors, nurses, clergy, parents and many pro-life Mississippians who are opposed to Initiative 26."

Jonathan F. Will, director of the Bioethics and Health Law Center at the Mississippi College of Law, said he, too, is concerned that people may not be able to understand the complexity of the amendment.

"My first thought, literally, was people aren't going to understand what this means ... what implications it has beyond abortions," he said.

Differing voices

What the amendment means, and whether it is either the most sensible measure or the most extreme and dangerous one, depends on whom you talk to in Mississippi.

Terri Herring, the national director for the Pro-Life America network and an advisory board member for Yes on 26, said the goal of the amendment is to give people the chance to say there is a better way than abortion. She also said the vote is a way to change the national conversation and push to give more rights to the unborn.

"In Mississippi, we have the opportunity to lead the way on a social justice issue," Herring said. "We may have been behind on civil rights, but we can be ahead on human rights, and that's what personhood is really all about."

But those opposed to the measure say that voting yes would be a huge mistake.

Cristen Hemmins, a mother from Oxford, has been speaking out against Initiative 26 because of what it could mean for her, her daughters and the ability of families to make the choices they want with their doctors.

"Whether or not you believe life begins at conception, this amendment goes too far," she said. "It is too ambiguous. It seems so obvious to me that it is far-reaching and it is going to be big government getting all up in my uterus."

Hemmins believes that passing the amendment would give the state too much control over women's reproductive rights.

Herring, on the other hand, thinks the amendment would be a way for Mississippi to be the first to support the rights of an unborn fetus while correcting contradictions in the state's constitution.

"If a woman was attacked and her unborn child was killed, it would be fetal homicide. That is considered a person," she said. "But on that very same day in the same area, a woman could go and have an abortion and kill her child, and nothing would happen. So we have a contradiction, and that is what we're trying to fix here."

But Hemmins believes that passing the amendment would be a "blight" on Mississippi, not a shining moment, and she cautions those who think this is just a local issue.

Overheard on CNN.com: 'Life at conception' amendment is backwards

Mississippi is the only state voting on a "personhood" initiative this year, but similar measures have gone on the ballot in other states and were defeated by wide margins. Other personhood measures are being planned for next year in Florida, Montana and Ohio, according to supporters. Efforts in at least five other states are in the planning stages.

"Apparently, they thought they needed to find a place more religious and more conservative, so they headed down here," Hemmins said. "But this is big government going too far in the poorest state in the country, with the highest teen pregnancy rate, the highest STD rate -- let's focus on fixing those things."

But many of those who support Initiative 26 say that defining life as the moment an egg is fertilized will allow women to really think about the decision of raising a child and open the door for a more successful adoption policy.

"We're trying to say there is another way besides abortion, that there can be a home for every child," Herring said. "Not every unwanted child has to die. There are over a million couples waiting to adopt. It's time to stop the senseless killing of children. We can provide these children, if people don't want them, to all of those who cannot have children themselves and stop the rush of people going to Russia, China and other areas to get children."

What would the measure mean?

Hemmins and others who work with No on 26 say the measure brings up more questions than answers, such as: What does it mean for women's reproductive rights? What does it mean about the decisions a woman can make with her doctor? Will it mean women will be at the mercy of the state when it comes to everything from taking certain birth control pills to trying to conceive if a couple is infertile?

But those in support of this measure say those questions are scare tactics used to sway votes.

"(They should) stop the fear-mongering and the tactics that are just talking about outrageous things that we do not believe will happen," Herring said. "This is really about saying, 'What did our forefathers intend when they used the word "person"?' I think very clearly, there is no way that long ago they had any intention of not including the unborn as a person. So in my mind, this is a historic vote, and it provides the people to have a voice in protecting life."

The vote is a way to start the conversation, Herring said, and laws that would help govern the definition change would come later.

"What legislation falls under that is yet to be determined," she said.

That is exactly the problem, according to opponents.

"Talking about the (implications) is just being smart; it's not fear-mongering," Hemmins said. "You don't pass an amendment like this and not think about what it might mean. That is just reckless."

Will, as a legal expert, said that if the amendment were to pass, it will probably face several legal challenges, but it also opens the doors for interpretation by local officials.

"The concern is that you could have local prosecutors that as soon as this amendment goes into place would say 'OK, well clearly this is the policy the people of this state want, so now I'm going to use our code to investigate miscarriages and IVF,' " Will said.

An area of particular concern for opponents is that it doesn't provide exception for victims of rape or incest who wish to terminate their pregnancy. Many states have varying bans on abortions but allow exceptions for such circumstances.

Hemmins, who was abducted, raped and shot twice by two men while she was in college, said it is "terrible" to not allow for any exceptions.

"I did not get pregnant, thank goodness, but if I had and Initiative 26 had been in place, I would have had no options," she said. "I would have been forced to have had this child by the government. I think it's a travesty in the United States of America that a state could force a woman against her will to bear a child."

Those supporting the amendment note that only a small fraction of people have to deal with that issue. A 2005 study by the Guttmacher Institute of New York shows that only 1% of women who had had an abortion said they had been raped. The study also showed that fewer than 0.5% became pregnant because of incest.

Herring said she has spoken to several rape victims who have been more haunted by their decision to abort their babies than by the rapes themselves. The Yes on 26 group even has videos posted of women speaking at local forums, discussing that exact issue.

One thing supporters and opponents of the amendment agree on is that this vote has the potential to change the entire debate about women's rights and abortion nationwide.

CNN's Vivian Kuo