The Marine Corps says it needs uniformity, especially during boot camp, and that beards pose risks. Sikhs say the rules are arbitrary and needlessly burden religious liberty.

WASHINGTON, D.C. (TIP): A Marine artillery captain named Sukhbir Singh Toor has been on a mission over the past year to become the first Sikh in the United States Marine Corps allowed to openly practice his religion while in uniform. During that time he has won a string of victories against the strict dress standards of the Marine Corps, and he can now wear the beard, long hair and turban required of a faithful Sikh while on duty. But recently, the Marine Corps dug in, refusing to allow him or any other Sikh to wear a beard on a combat deployment or during boot camp, saying that beards would hinder the corps’s ability to function and put lives at risk.

On Monday, Captain Toor and three other Sikhs sued the Marine Corps in U.S. District Court for the District of Columbia, saying the corps’s refusal to grant a religious waiver is arbitrary and discriminatory, and violates the constitutional right to free exercise of their religion.

“I just want to move on, so I can do my job,” Captain Toor, 27, said in an interview from his base in Twentynine Palms, Calif., before the suit was filed. “There is no reason I should have to sacrifice my faith in order to serve my country.” Joining him in the lawsuit are three prospective Marine recruits who have been told they must shave their beards and cut their hair for boot camp, where all Marines receive basic training, and only afterward would be able to apply for a religious exemption.

The lawsuit is emblematic of the larger struggle the tradition-bound military faces in trying to attract personnel in an increasingly diverse nation, while preserving practices that took root when its ranks were almost entirely white, male and Christian. At issue is the long-simmering tension between constitutional guarantees of individual rights and the military’s need to maintain an effective fighting force that at times must impinge on those rights. The back and forth over religion has been evolving since at least 1981, when an Orthodox rabbi serving in the Air Force sued the service over the right to wear a skullcap. Current law requires that the military not restrict individual exercise of religion except when a “compelling government interest” is at stake, and in those cases, to use the “least restrictive means” possible.

What counts as a compelling government interest, or as the least restrictive means, is at the center of the case.

The Marine Corps declined to comment on the lawsuit. In prior administrative decisions concerning Sikh turbans and beards, Marine leaders have cited two interests it said were compelling. One is uniform appearance in the ranks, which the corps argues is crucial to good order and discipline.

“Uniformity is more than the mere outward expression of unity with the team; it is a tool that constantly reminds each Marine of the team to which they are committed and a signal to other Marines of the depth of that commitment,” the Marine Corps said in response to Captain Toor’s first request for an accommodation in June. Tampering with that commitment, it warned, could cost lives.

Second, the Marine Corps has said, beards might hinder Marines’ physical ability to do their duties by keeping them from safely wearing gas masks.

That is why Captain Toor and other Sikhs currently cannot wear beards when deployed in any of 39 countries that are considered potentially hostile, including Algeria, Israel, Turkey, Uganda and Cuba. Col. Kelly Frushour, a Marine spokeswoman, said the risks in foreign deployments could change rapidly. “Accordingly, Marines in a combat zone must be prepared to don a gas mask at any time with little or no notice,” she said.

In their suit, the Sikhs counter that the Marine Corps routinely deploys men to combat zones who have permission to wear beards because of medical conditions or because they are part of Special Operations units. And the corps’s beard rules would require the Sikhs to shave even in countries where the risk of chemical attack is so low that Marines deployed there are not equipped with gas masks. The Army made similar safety arguments against a Sikh soldier in 2015 but relented in 2016 after the soldier sued. About 100 Sikhs currently serve in the Army and Air Force wearing full beards and turbans, and many have been deployed to combat zones. In interviews, they have reported no issues. The American military now grants more religious exemptions to uniform and grooming standards than ever before, allowing hijabs for Muslim women, long hair for a small Christian sect, and beards for a few practicing Norse Heathens. But the Marine Corps has for generations fought changes after other branches embraced them. It was the last service branch to allow Black men to enlist, and it balked at a 2015 mandate to allow women to serve in combat.

In the case of the Sikhs, the Marine Corps has dug in over more than just practical considerations. It also says beards and turbans are a potential threat to a more abstract concept of unity.

The 13 weeks of boot camp are the crucible where ordinary citizens are turned into Marines, taking away nearly all individual identity — phones, personal clothes, hair styles and even the word “I”: Drill instructors force recruits to refer to themselves only as “this recruit.”

“This transformative period sets the foundation for further service by breaking down individuality and training recruits to think of their team first,” the Marine Corps wrote in February when it denied an accommodation for one of the prospective Sikh recruits, Aekash Singh. “Uniformity is a key component of this process. Consequently, limiting exceptions during this transformative process constitutes the least restrictive means to further the government’s compelling interests.”

Mr. Singh and two other prospective recruits, Jaskirat Singh and Milaap Singh Chahal, declined to be interviewed. In a statement, they said: “We remain ready to meet the high mental and physical standards of the Marine Corps because we want to serve our country alongside the best. We cannot, however, give up our right to our religious faith while doing so.”

In the suit filed on Monday, their lawyers argued that the Marine Corps routinely allows other recruits into boot camp who do not fit homogeneous appearance standards. Women are allowed to keep their long hair during training, and the corps recently loosened restrictions on tattoos, allowing recruits to have ink covering everything but their hands, head and neck.

The corps said the change in the tattoo policy was meant “to balance the individual desires of Marines with the need to maintain the disciplined appearance expected of our profession.” The Sikhs say in their lawsuit that “it is perverse to claim that respecting ‘the individual desires of Marines’ to have full-body tattoos is consistent with mission accomplishment, but that respecting Marines’ desires to be faithful to God is somehow risky.”

Giselle Klapper, a civil rights attorney with an advocacy group, the Sikh Coalition, who is one of the lawyers representing the plaintiffs, said that the coalition tried for more than a year to negotiate a solution with Marine Corps leaders, but that the corps had been unreceptive.

She predicted that her clients would prevail, as Sikhs have in the other service branches, but said she was disappointed that they had to take the issue to court. “We feel we have run out of other options,” she said. “People’s lives have been put on hold. How long do they have to wait?”