Updated at 4:44 p.m. ET
Nebraska Gov. Dave Heineman has signed two landmark abortion bills into law that both sides of the abortion debate say are firsts in the country.
One bars abortions at and after 20 weeks of pregnancy based on assertions that fetuses feel pain at that time. The current standard is viability, or when a fetus is able to survive outside the womb.
Abortion-rights advocates say that is a clear break with court precedent and it won't withstand a court challenge. Supporters of the ban see an opening in previous court rulings.
Viability is determined on a case-by-case basis but is generally considered to occur at 22 to 24 weeks.
The other bill signed by Heineman will require doctors or other health professionals to assess whether women have risk factors that could lead to mental or physical problems after an abortion.
Nebraska lawmakers approved that law, another first-of-its kind, Monday. Legislators passed the law asserting that fetuses feel pain at 20 weeks on Tuesday.
If upheld by the courts, the law could change the foundation of abortion laws nationwide.
Passed by the state's officially nonpartisan legislature, the law is partially meant to shut down one of the few late-term abortion providers in the country,. He attracted attention after his friend and fellow late-term abortion provider Dr. George Tiller was in Kansas last year.
Kansas lawmakers, concerned Carhart was considering opening a clinic there after Tiller's death, passed a law to prevent that, but Gov. Mark Parkinson, who supports abortion rights, hasn't acted on it yet.
Nebraska's law is sure to be challenged in court. One national abortion-rights group called it "flatly unconstitutional."
"It absolutely cannot survive a challenge without a change to three decades of court rulings," said Nancy Northup, president of the Center for Reproductive Rights. "Courts have been chipping away at abortion rights...this would be like taking a huge hacksaw to the rights."
She indicated her group might challenge the law in court. Carhart has also suggested he might challenge the law.
But abortion opponents say a 2007 U.S. Supreme Court ruling upholding a federal ban on certain late-term abortions opens the door for such legislation because it suggests states have an interest in protecting fetuses. They also say the law makes sense given what they say is new scientific evidence that fetuses feel pain.
"The Nebraska legislature has taken a bold step which should ratchet up the abortion debate across the nation," Nebraska Right to Life director Julie Schmit-Albin said. "What we didn't know in 1973 in Roe versus Wade ... we know now."
It is unclear how many fewer abortions might be performed in the state because of the law - doctors aren't required to report at what stages in pregnancies they perform abortions. Carhart is believed to be the only doctor in the state that performs abortions at or after 20 weeks; Planned Parenthood does not perform abortions at 20 weeks.
Abortion opponents say studies and testimony from doctors prove fetuses feel pain at 20 weeks. The American College of Obstetricians and Gynecologists, however, says it knows of no legitimate evidence that fetuses experience pain.
"There is certainly no solid scientific evidence establishing that a fetus can perceive pain at these earlier stages, so any court decisions to uphold such broader laws could only do so by disregarding the importance of good scientific evidence," said Caitlin Borgmann, a law professor at The City University of New York.
The U.S. Supreme Court would have to overturn earlier abortion-related rulings to uphold the Nebraska law, Borgmann said, including a 1992 ruling in Planned Parenthood v. Casey that upheld the right of women to have abortions before fetuses were viable.
Abortion supporters and opponents agree the key vote would come from Justice Anthony Kennedy, who sided with the majority in Planned Parenthood v. Casey but is a moderate conservative.
Mary Spaulding Balch, legislative director for national Right to Life, said the key question for the law's supporters is "do we have Kennedy?"
She said she believed there was a good chance the law would be upheld, and if it was, it would provide greater protection for unborn children.
"It says the state has an interest in the unborn child before viability," she said.
The switch from viability to fetal pain in justifying abortion limits isn't the only aspect of the Nebraska law that raises legal issues.
The law also bars women from having abortions after 20 weeks because of mental health problems. The only exceptions to the ban would be if a woman was near death or at risk of irreversible physical harm.