Alabama cannot prosecute doctors and reproductive health organizations for helping patients travel out of the state to obtain abortions, a federal judge ruled on Monday.

Alabama has one of the strictest abortion bans in the country, and in 2022 its attorney general, Steve Marshall, a Republican, raised the possibility of charging doctors with criminal conspiracy for recommending abortion care out of state.

Multiple clinics and doctors challenged Mr. Marshall’s comments in court, accusing him of threatening their First Amendment rights, as well as the constitutional right to travel. The Justice Department under the Biden administration had also weighed in with support for the clinics, arguing that “threatened criminal prosecutions violate a bedrock principle of American constitutional law.”

On Monday, the judge, Myron H. Thompson of the Middle District of Alabama, in Montgomery, ruled that Mr. Marshall would be violating both the First Amendment and the right to travel if he sought prosecution.

“It is one thing for Alabama to outlaw by statute what happens in its own backyard,” Judge Thompson, who was named to the court by President Jimmy Carter, wrote in his 131-page opinion.

“It is another thing,” he added, “for the state to enforce its values and laws, as chosen by the attorney general, outside its boundaries by punishing its citizens and others who help individuals travel to another state to engage in conduct that is lawful there but the attorney general finds to be contrary to Alabama’s values and laws.”

Judge Thompson described a hypothetical scenario in which a bachelor party from Alabama could be prosecuted for casino-style gambling in Las Vegas, which is illegal in Alabama.

“As the adage goes, be careful what you pray for,” he wrote.

Travel to other states to obtain an abortion, or abortion pills, has significantly increased since the Supreme Court overturned Roe v. Wade. More than 171,000 patients traveled for an abortion in 2023, compared with 73,100 in 2019, according to the research organization Guttmacher Institute.

Mr. Marshall repeatedly defended his position in court, arguing that he retained the ability to prosecute a conspiracy that took place in Alabama and that the legality of abortion laws in other states did not matter. (He does not appear to have charged anyone in such a case.)

“The right to travel, to the extent that it is even implicated, does not grant plaintiffs the right to carry out a criminal conspiracy simply because they propose to do so by purchasing bus passes or driving cars,” Mr. Marshall wrote in one filing.

Republican-led states, like Alabama, generally have the most restrictive abortion laws in the country. Some of those states are now taking legal steps to stop out-of-state efforts to help residents obtain abortions.

Louisiana, which passed a law last year designating abortion pills as dangerous controlled substances, has charged both a Louisiana mother and a New York doctor with violating the state’s abortion ban. (New York has declined to extradite the doctor.)

And this month, a New York county clerk blocked Texas from filing legal action against the same doctor. New York has an abortion shield law that prevents penalties against abortion providers who use telemedicine to send medications to other states.

The Alabama ruling could be appealed, as the judicial system continues to grapple with the fallout from Roe. In June, the Supreme Court temporarily allowed for emergency abortions in Idaho, though it did not weigh in directly on the state’s abortion ban.

Alabama, where voters approved a constitutional amendment in 2018 aimed at protecting the rights of unborn children, has been at the center of the debate over reproductive medicine and abortion access. It has one of the strictest abortion bans in the nation, with an exception only if the life of a pregnant woman is at risk. It also allows for doctors to be charged with felonies that carry sentences of up to 99 years in prison.

And its anti-abortion amendment was at the heart of a State Supreme Court decision last year that found that embryos could be considered children, a decision that briefly paralyzed fertility treatments in the state and thrust the issue of in vitro fertilization into the national spotlight.

The clinics that first challenged Mr. Marshall’s comments, in 2023, included the Yellowhammer Fund, an organization founded in Tuscaloosa that helps fund and support abortion access in the Deep South, and the West Alabama Women’s Center in Tuscaloosa, now known as WAWC Healthcare. The plaintiffs also included Dr. Yashica Robinson, an obstetrician-gynecologist in Huntsville.

In court filings, they said they either had stopped operating an abortion fund or had begun declining to answer questions about how patients could seek care out of state. Collectively, the plaintiffs still receive several calls a week asking for help; the court ruling on Monday put the figure at as many as 95 a week.

“Every day was agonizing,” said Kelsea McLain, the health care access director for the Yellowhammer Fund. The ruling, she said, brought “just an overwhelming sense of relief.”

“We are free to do exactly what we feel called to do, in ways that we are experts in,” she added. “People won’t be alone.”

Mr. Marshall’s office did not immediately respond to a request for comment.

Notably, in a 2022 opinion concurring with the decision to overturn Roe, Justice Brett Kavanaugh wrote that he did not believe a state could constitutionally bar a resident from traveling for an abortion. Judge Thompson noted this in his ruling on Monday.

Abbie VanSickle contributed reporting.