The American Humanist Association said Thursday (Sept. 4) that an airman at Nevada’s Creech Air Force Base who crossed out “so help me God” in the oath the Air Force requires servicemen and women to sign was told in August he must sign it as is or leave the Air Force.

The AHA’s Appignani Humanist Legal Center sent a letter to the Air Force on the airman’s behalf demanding he be allowed to sign a secular version of the oath. The U.S. Constitution allows freedom of religious beliefs and prohibits religious tests for holding public office or public trust, the letter states.

The airman’s name is being withheld by AHA.

“The Supreme Court has held on a number of occasions that it is unconstitutional to force anyone to take an oath that affirms the existence of a supreme being,” said Monica Miller, an attorney for AHA and author of the letter. “Numerous federal courts have specifically held that forcing an atheist to swear to God violates the Free Exercise Clause as well as the Establishment Clause.”

But a spokeswoman for the Air Force told the Air Force Times the oath cannot be changed without an act of Congress.

“Reciting ‘So help me God’ in the re-enlistment and commissioning oaths is a statutory requirement,” Air Force spokeswoman Rose Richeson said.

According to Richeson, the oath requirement was changed in October 2013. Before then, an exception permitted airmen to omit the words “so help me God” if they had “personal reasons.”

Miller said the AHA is prepared to sue the Air Force. “But given that the law is so well-settled on this issue, I would hope that litigation is not necessary,” she said.

Last year, AHA represented an officer trainee at Maxwell Air Force Base who was compelled to agree to the same religious language. The matter was resolved “quickly in our favor after the Air Force realized they could not compel him to affirm the existence of a supreme being,” Miller said.

The airman’s case was brought to the attention of the AHA by the Military Association of Atheists and Freethinkers, which promotes the rights of nonbelievers in the military.

“This Airman shows integrity, commitment to the nation, and respect for religion in standing firm for a secular oath that reflects his true values and intentions,” said Jason Torpy, MAAF’s president.