When an active-duty Marine was given a Marine Corps training document describing "potential risk indicators" commanders should look for to prevent loss of life among service members, he found one checkbox that didn't seem to fit. Among warning signs like substance abuse and prior suicide attempts was "lack or loss of spiritual faith."

Concerned that this was a discriminatory policy, the Marine notified the Military Religious Freedom Foundation (MRFF), a nonprofit dedicated to keeping religion separate from the U.S. military. The organization, which told me that it plans to sue the U.S. Marines unless the government backs off this policy, says this is the military's latest effort to discriminate against service members who don't believe in God.

Advocates for the policy say the military is simply doing everything it can to promote emotional well-being among troops, especially in the face of its growing suicide epidemic. (Last year, the U.S. military saw more active duty soldiers commit suicide than die in combat — 48 of them Marines.)

"The whole concept of judging service members based on their spirituality is completely unconstitutional," says Mikey Weinstein, a former Air Force officer and founder and president of MRFF. "This country was founded on a very critical principle — the Founding Framers looked at the horrors that occurred throughout history by mixing religion and war, and they said, 'We're going to separate church and state.' And that means they cannot test for religion in the military."

The training document does not specify how a commander is supposed to test whether a Marine has spiritual faith — Weinstein claims that in a preliminary computer test, Marines are asked questions like "what do you think of when you see a sunset?" — but it does say that when a Marine is identified as high risk, a "Force Protection Council" will interview, monitor, and recommend further action at the council's discretion. (The Marine Corps did not respond to our questions about this policy.)

This is hardly the first time the military has tried to govern the religion of its service members. Until 1972, each U.S. service academy required soldiers to attend weekly religious services — and only Protestant, Catholic, and Jewish worship services were available, according to Blake Page, special assistant to the president of MRFF. Until 2011, the Army required soldiers to take a survey that measured "spiritual fitness," and soldiers who failed were told that "improving your spiritual fitness should be an important goal."

Defending the test in 2011, Brig. Gen. Rhonda Cornum told NPR, "Researchers have found that spiritual people have decreased odds of attempting suicide, and that spiritual fitness has a positive impact on quality of life, on coping and on mental health." The Marine Corps document also notes that its risk indicators for early death are "derived from scientific studies."

But Page argues that this logic is flawed, because studies that come to the conclusion that religion reduces dangerous behavior "only measure religiosity through religious service attendance. This is a failed conclusion, because attending a regular social activity of any sort produces the same external community of support that a religious community provides."

Paul Loebe, an active-duty Marine and the military director for American Atheists, agrees with that sentiment. He says that in his eight years of service, the Marine Corps never required him to take a religious test — although "they do have one available" — but notes that he was initially denied the right to put "atheist" on his dog tags. When Loebe tried to seek counseling from a chaplain, he was asked to end every session with a prayer. "It made the whole situation very uncomfortable, especially when I had a very serious problem to deal with," Loebe says.

Last month, Rep. Rob Andrews (D-N.J.) tried and failed to amend the 2014 National Defense Authorization Act so that non-theist chaplains could be part of the military — a proposal that drew fierce opposition from some Republicans. Rep. Mike Conaway (R-Texas) told The Huffington Post, "I can't imagine an atheist accompanying a notification team as they go into some family's home to let them have the worst news of their life and this guy says, 'You know, that's it — your son's just worms, I mean, worm food.'"

But Loebe says that when he was in charge of drafting a Force Preservation Policy for his unit — similar to the one found to discuss spiritual faith — he thought that exposing everyone's private religious beliefs would have eroded trust among his fellow Marines. A religious requirement "does quite the opposite of 'preserving the force,'" he says.

"There are many service members past and present that have served honorably and continue to serve without believing in God, and there's no reason to believe they can't continue to do that today."