A mainland watchdog group is crying foul over a “God bless the military” sign on the Marine base in Kaneohe, claiming the display violates the First Amendment.

On Thursday the Military Religious Freedom Foundation sent an email to Col. Sean Killeen, commanding officer of Marine Corps Base Hawaii, asking that the sign be moved to the chapel grounds or removed.

The advocacy group claims the sign is a “brazen violation” of the Establishment Clause of the Constitution, which forbids the government from unduly expressing preference for religion over nonreligion.

The group’s email to Killeen said the sign “sends the clear message that your installation gives preference to those who hold religious beliefs over those who do not.”

The sign, at an intersection near the marina, reads in full, “God bless the military, their families, and the civilians who work with them.”

The foundation is a nonprofit with a mission to protect the religious freedom of U.S. military members. The organization boasts of numerous achievements over the years on its website, including pressuring the U.S. Air Force to drop the requirement that enlistees state “so help me god” in their enlistment oath; compelling a South Carolina-based Marine fighter attack squadron to change its name from “Crusaders” to “Werewolves”; and pointing out the use of Nazi symbols by U.S. Marines serving in Afghanistan, prompting an apology from then-Marine Corps Commandant James Amos.

The organization’s founder, Mikey Weinstein, said by phone from New Mexico on Thursday that 23 Marines, from enlisted to officers, have complained about the sign to his organization over the past two weeks.

He said the sign stands out “like a tarantula on a wedding cake,” adding, “They know it’s wrong. We’ve respectfully asked the commander to do the right thing, move it to the chapel grounds or take it down.”

He said should the commander allow the sign to remain, then he must allow other religious signs, such as one that says “no god blesses the troops,” which would be demoralizing.

He called the sign a “smoking gun” for religious tyranny on base.

“Why is Col. Killeen’s command climate so toxic and noxious that we have 23 Marines coming to us, asking us to please tell the emperor that he has no clothes?” he asked.

He said the Marines — 21 of whom are Protestant — have not used the chain of command to lodge a complaint because they fear reprisal.

Capt. Tim Irish, spokesman for Marine Corps Base Hawaii, said the commanding officer received an emailed complaint about the sign and ordered his staff to research the sign’s origin and its compliance with existing regulations.

He said the Base Inspector’s Office is also investigating whether there have been complaints in the past about the sign, which was erected in 2001.

“MCBH will exercise due diligence to ensure compliance with existing regulations and law, including the Establishment Clause of the U.S. Constitution,” he said in an email.

Brian Brazier, a constitutional law attorney in Honolulu who is not involved in the dispute, said the sign falls in a gray area of the Establishment Clause.

“There’s a legitimate place for religion on federal and state property as long as the specific religion is not being favored over other religious viewpoints,” he said. “If all viewpoints are given equal access to the space, then it probably doesn’t present a constitutional problem.”

He said both those who support the sign as a way of supporting the troops and those who oppose the sign on religious grounds have legitimate arguments.

“If a different religion were to put up a sign in the same location and that one was ordered down, and the ‘God bless the troops’ was allowed to stay up, that presents a problem,” he said.

The watchdog group shared one email from an anonymous Marine that said many Marines on base are grateful to the organization for making their feelings known to the commander.

“Were we to do it, there would be severe consequences to us and our families,” the Marine wrote.