WASHINGTON (NEXSTAR) — The U.S. Supreme Court is gearing up to hear the biggest abortion case in decades on Wednesday.

It centers on a Mississippi law that bans the procedure after 15 weeks of pregnancy. Supporters of the measure are asking the justices to end the constitutional right to abortion, and opponents worry this could be the case and the court to do it.

“The government cannot force her to bear a child against her will,” said Rob McDuff, an attorney with the Mississippi Center for Justice.

McDuff, who is part of the team representing Mississippi’s lone abortion clinic, said that’s what’s at stake when the nation’s highest court takes up the state’s ban.

“A woman has the right to choose whether to carry her pregnancy to term,” he said.

McDuff argues the high court has already decided in Roe v. Wade and reaffirmed in Planned Parenthood v. Casey that states cannot ban abortions prior to a fetus’ viability, which is around 24 weeks.

“You shouldn’t be able to go back and overturn settled rights simply because the composition of the Supreme Court has changed,” he said.

But that’s exactly what anti-abortion advocates want, and many expect the court’s new 6-3 conservative majority to overturn Roe.

“We have an opportunity to save literally millions and millions of lives in the future if this case is to be ruled upon favorably,” said Gov. Tate Reeves, R-MS.

Reeves shepherded the law in question through the state legislature as Senate president, and fellow GOP governors, like South Dakota’s Kristi Noem, support it.

“We actually have to go out and take actions that defend lives and save lives,” Gov. Noem said.

The justices aren’t expected to rule until next summer, but if they overturn Roe, many states, including Mississippi and South Dakota, already have measures in place that would automatically ban abortion.

If the high court does not formally overturn Roe, a decision weakening the two precedents would open the door to new restrictions, like bans on some early-stage abortions.