BOISE, Idaho (AP) — An Idaho law banning nearly all abortions would take effect if the U.S. Supreme Court overturns Roe v. Wade, the landmark 1973 ruling that declared a nationwide right to abortion.

The court with a 6-3 conservative majority on Wednesday will hear arguments over a Mississippi law that bans abortions after 15 weeks. That law is on hold following a 5th U.S. Circuit Court of Appeals ruling.

The Mississippi law is also at odds with a 1992 Supreme Court ruling that states can't prevent women from terminating pregnancies before viability, around 24 weeks.

If those rulings are overturned, as Mississippi officials argue they should be, states would decide whether to regulate abortion before a fetus can survive outside the womb.

That would trigger an Idaho law, passed in 2020, banning all abortions except in cases of rape, incest or to protect the life of the mother. That law would take effect in Idaho 30 days after the Supreme Court decision.

That law passed the Republican-dominated Idaho House and Senate with no Democratic support, and was signed into law by Republican Gov. Brad Little. Under the law, criminal punishment would be a felony and apply to the person performing the abortion, not the woman.

Little in July signed onto an amicus brief with Republican governors from 11 other states supporting the Mississippi law now before the Supreme Court.

Then-President Donald Trump appointed three conservative justices to the U.S. Supreme Court, including last year appointing Justice Amy Coney Barrett after the death of Justice Ruth Bader Ginsburg. Before that, the court had never before agreed to hear a case over a pre-viability abortion ban.

Idaho lawmakers seeing the change on the Supreme Court the last several years have passed abortion-ban laws with trigger mechanisms.

"I'm optimistic," said Republican Sen. Todd Lakey, who sponsored the 2020 law. "I think the situation on the Supreme Court has improved in regard to pro-life issues. But you're talking about precedent and other things the court will evaluate, so I can't really predict where they'll come down. But I'm hopeful that they will eventually, if not in this case then in another case, overturn Roe v. Wade."

Only one justice, Clarence Thomas, has publicly called for Roe to be overruled.

Planned Parenthood Alliance Advocates officials didn't immediately return a text message or call from The Associated Press on Monday.

A different law passed earlier this year by Republicans in the House and Senate and signed by Little, which also has a 30-day trigger mechanism, would ban abortions once a fetal heartbeat can be detected.

It does not appear that law would be triggered by the Mississippi case. It would be superseded by the more restrictive 2020 law if Roe v. Wade is overturned. If the court doesn't overturn Roe v. Wade but upholds the Mississippi abortion ban at 15 weeks, it would not appear to be restrictive enough to trigger the Idaho law. The Idaho law also contains language that causes it to be triggered by an appeals court ruling, not a Supreme Court ruling.

According to the Guttmacher Institute, a research organization that supports abortion rights, a ruling that overturned Roe and the 1992 case of Planned Parenthood v. Casey would lead to outright bans or severe restrictions on abortion in 26 states.

The institute said that states unlikely to ban abortion that would have the nearest provider for people from Idaho would be Washington, Oregon, Nevada and Colorado.