Updated at 9:35 a.m. ET

A federal judge in Mississippi has permanently blocked one of the most restrictive abortion laws in the country — a ban on the procedure after 15 weeks of gestation.

The law was signed by Republican Gov. Phil Bryant in March, but a court quickly imposed a temporary block, which was extended several times. The order was set to expire Monday.

"The ban's lawfulness hinges on a single question: whether the 15-week mark is before or after viability," District Judge Carlton W. Reeves wrote in his Tuesday ruling.

"The record is clear: States may not ban abortions prior to viability; 15 weeks [since a woman's last menstrual period] is prior to viability," he wrote.

The law proposed exceptions in the case of a medical emergency or severe fetal abnormality. Mississippi argued that because of these exceptions, the law was a "regulation" and did not place an "undue burden" on a woman's right to choose.

"This act is a ban. It is not a regulation," Reeves wrote in response to the state's argument.

Reuters reports the ruling effectively blocks a similar ban on abortions after 15 weeks gestation in Louisiana, which was set to take effect if the Mississippi law survived.

Mississippi Attorney General Jim Hood, a Democrat, said he knew the law would be difficult to defend in court. "We know that bans below 20 weeks have been struck down," he said in March. "We expect an immediate and expensive legal challenge."

Reeves acknowledged this sentiment in his ruling.

"The State chose to pass a law it knew was unconstitutional to endorse a decades-long campaign, fueled by national interest groups, to ask the Supreme Court to overturn Roe v. Wade," Reeves wrote. "This Court follows the commands of the Supreme Court and the dictates of the United States Constitution, rather than the disingenuous calculations of the Mississippi Legislature."

"The Mississippi Legislature's professed interest in 'women's health' is pure gaslighting," he wrote in a citation. "Its leaders are proud to challenge Roe but choose not to lift a finger to address the tragedies lurking on the other side of the delivery room: our alarming infant and maternal mortality rate."

The Supreme Court has rejected a number of states' attempts to limit abortions to women 15 or fewer weeks pregnant, including a North Dakota law that banned abortions at six weeks and an Arkansas law that banned them at 12 weeks.

"I am committed to making Mississippi the safest place in America for an unborn child," Bryant tweeted after signing the ban.

The governor set a goal in a 2014 State of the State Address to free the state of abortion "completely."

Neither Bryant nor the Mississippi Department of Health — a defendant in the case — issued a statement immediately following the Tuesday ruling. Reuters reports that Bryant's office said the governor was traveling.

Abortion rights proponents celebrated the ruling.

"Our victory today means that women in Mississippi will maintain the ability to make their own decisions about whether and when to terminate a pregnancy," said Nancy Northup, president and CEO of the Center for Reproductive Rights, which filed the lawsuit on behalf of Jackson Women's Health Organization, the last remaining abortion clinic in the state.

"Today's decision should be a wake-up call for state lawmakers who are continuously trying to chip away at abortion access. Such bans will not stand in a court of law," she said in a news statement.

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