BATON ROUGE — Louisiana’s Democratic governor signed one of the country’s strictest abortion bans Thursday a day after the state legislature passed the measure, joining a coterie of conservative state executives who have endorsed stringent measures this year.

Louisiana’s measure is the first of the drumbeat of bans this year to receive the imprimatur of prominent local Democrats, whose support for the controversial legislation has provoked anger from party members nationwide who see it as a betrayal in the battle over abortion rights.

State lawmakers voted 79 to 23 on Wednesday to pass the bill, with the support of more than a dozen Democrats. They rejected amendments that sought to make the law more lenient, including one that would have added an exception to the ban for cases of rape and incest.

“I call on the overwhelming bipartisan majority of legislators who voted for it to join me in continuing to build a better Louisiana that cares for the least among us and provides more opportunity for everyone,” Gov. John Bel Edwards said in a statement after it was passed. He did not hold a public signing ceremony for the bill, and his office declined to comment on it further.

Nationally, however, Edwards; state Sen. John Milkovich, the Democrat who sponsored the bill; and other antiabortion Democrats have become unlikely intraparty combatants in a debate that has grown increasingly partisan.

As the party has shifted left in recent decades, its leaders have increasingly signaled that members who oppose abortion rights are fundamentally out of step with the Democratic platform.

Since the presidency of Ronald Reagan, the issue has become increasingly divisive, especially in judicial confirmations, said Sherry Colb, a professor at Cornell Law School. Now, parties tend to use a judge’s stance on abortion as a litmus test to decide whether they will support a particular nominee, she said.

But in Louisiana, antiabortion sentiment has long been part of the cultural milieu. The issue is not nearly as divisive as it is on the national stage.

The legislation, a “heartbeat” ban, resembles other bills passed this year in deep-red states that could outlaw abortions after an ultrasound is able to detect the electric pulsing of what will become a fetus’s heart, a milestone that can come at six weeks — before many women even know they are pregnant.

The ban joins a number of antiabortion laws already on the state’s books, many of which made it there with bipartisan support.

In 2006, a Democratic Louisiana state senator sponsored a “trigger law” that would automatically ban abortions, except when birth threatens a mother’s life, in the event that the Supreme Court overturns its Roe v. Wade decision. Then-Gov. Kathleen Blanco, also a Democrat, signed it into law, ensuring Louisiana would be among the first states to outlaw abortion should the high court reverse course.

The state also prohibits public funding for abortions, and most private insurers there do not cover the procedure, which means it can be costly. Other laws, such as requiring women to undergo an ultrasound and submit to a mandatory scripted counseling session, have also made abortions less accessible, particularly for those who must travel to a clinic from afar.

Another measure making its way through the legislature would let the public vote on a constitutional amendment that would prevent the state from protecting the right to an abortion or requiring funding for it.

The bill’s sponsor, state Rep. Katrina Jackson, another Democrat, said in an interview with The Washington Post before the vote that she planned to support the six-week ban, too. Her party’s preferences are no match for her own deeply held religious beliefs, she said.

“I don’t believe in being a cookie-cutter legislator, which means you say, ‘Oh, what’s the party doing?’ " she said. “When you have a sincerely held belief, you stand for that belief. That doesn’t mean you abandon your party. That doesn’t mean that you abandon anyone. That means that you understand that a one-size-fits-all approach to legislature doesn’t work.”

Discussion of a new ban and the laws already in action have “made Louisiana an extremely hostile place” for women trying to obtain abortions and for doctors trying to provide them, said Michelle Erenberg, the executive director of Lift Louisiana, which advocates for women’s health and abortion access.

The state’s three remaining abortion providers have already begun receiving calls from women asking whether abortion is still legal, she said.

Katie Caldwell, the clinic coordinator at the Women’s Health Care Center in New Orleans., said that “things have become incrementally worse, and then suddenly catastrophic.”

The Louisiana branch of the American Civil Liberties Union said in a statement that “Louisiana politicians have now sunk to a new low.”

The ban will not go into effect right away — and it may even end up languishing for years in legal purgatory. It will take effect only if a federal court upholds a near-identical ban in neighboring Mississippi. Just like other bans, Mississippi’s legislation has faced vigorous legal challenges. On Friday, a judge temporarily blocked it.

Earlier this year, a federal judge halted Kentucky’s similar heartbeat measure, questioning the law’s constitutionality. All the bans are part of a barrage of new restrictions — largely in states in the South and the Midwest — championed by religious conservatives and meant to spark a court fight that would challenge Roe, which legalized abortion nationwide in 1973.

Before any of the cases makes it to the Supreme Court, an appeals-court judge would have to defy federal precedent and uphold one of the bans. The process could take years, and on Tuesday, Supreme Court justices issued a compromise decision on an Indiana law — signaling they might proceed slowly on other abortion cases.

In Louisiana, the nation is seeing some of the last remaining antiabortion Democrats, a class of politician that has grown obscure in recent decades.

Edwards has been a high-profile member of that group since he was elected governor in 2015. Like other antiabortion Democrats, he likes to say he’s “pro-life for the whole life,” because he opposes abortion and supports policies such as Medicaid expansion and a higher minimum wage. In his post-vote statement, he said he believes that “being pro-life means more than just being pro-birth.”

The Army veteran and Catholic has said he traces his long-held views on abortion to his faith — and so do many of his constituents, he said.

“That’s the way I was raised,” Edwards said in an October episode of his monthly radio show. “I know that for many in the national party, on the national scene, that’s not a good fit. But I will tell you, here in Louisiana, I speak and meet with Democrats who are pro-life every single day.”

One of Edwards’s fellow Democrats, state Rep. Royce Duplessis, disagrees with his governor’s stance. In an interview, he said that the government has no right to interfere in decisions about a woman’s health care and that this bill “absolutely goes too far.” He opposes it, he said, and not because of the national party’s marching orders.

“It has nothing to do with party for me,” he said. “It has nothing to do with party lines for me. I tend to stay consistent with what I believe, and that’s respect for women, respect for women’s health.”

Countrywide, Democratic voters are more in line with Duplessis than with antiabortion lawmakers such as Edwards, Milkovich and Jackson.

Today, three-quarters of Democrats believe abortion should be legal in all or most cases, a figure that has increased by more than 10 points since the mid-1990s, according to the Pew Research Center. But this shift has left some more-conservative lawmakers and voters, whom the party had long welcomed, feeling alienated.

It is yet another example of phenomenon so often observed it has become a cliche: The country’s political parties are more polarized, the electorate more divided.

“It’s almost like the Democratic Party is this club, and there are rules to this club. And you can’t violate the rules,” said Colb, the professor, who clerked for Supreme Court Justice Harry A. Blackmun, author of the Roe decision. “There’s a sense that we’re not going to tolerate intolerance.”