NASA is being accused of discriminating against some of its Christian employees after allegedly telling a prayer club that it was no longer allowed to mention the name “Jesus” in a newsletter.

The Liberty Institute, a religious freedom advocacy group, is representing the employees and on Monday threatened to file a federal lawsuit if NASA does not remove the alleged restriction.

The employees are 16 members of the Praise and Worship Club at the Johnson Space Center in Houston, according to the institute, and submit meeting announcements to the center’s JSC Today email newsletter to invite other employees to attend the club’s upcoming gatherings.

Last May, the newsletter ran the group’s announcement saying the theme for its upcoming meeting would be “Jesus is our life!”

A NASA attorney allegedly told the employees they were not allowed to include “Jesus” in future advertisements because NASA would be violating the Establishment Clause, which prevents government entities from promoting one religion over another. The employees say their speech is private and their announcements do not represent NASA’s official stance, so NASA censoring them from saying “Jesus” in the newsletter is an illegal restriction of their religious freedoms.

The club has been meeting since 2001, according to the Liberty Institute, and members currently gather during their lunch hours to discuss their faith and sing Christian songs.

“We are shocked that NASA would censor the name of Jesus from our Praise and Worship Club’s announcement,” JSC Praise and Worship club spokesperson Sophia Smith said in a statement released by the Liberty Institute. “NASA has a long history of allowing the religious speech of its employees, so why would they ban ‘Jesus’ from our announcements?”

The Liberty Institute noted NASA astronauts have famously made high-profile religious comments in the past. Notably, Scott Carpenter said “Godspeed, John Glenn” when Glenn became the first American to orbit the planet in 1962 and Bill Anders, Jim Lovell and Frank Borman read from the Book of Genesis as they orbited the moon on Christmas Eve, 1968.

The institute argues the ban is discriminatory, claiming the newsletter still publishes other “generic religious references.” The Praise and Worship Club’s announcements are also still published, the institute claims, though the club stopped mentioning Jesus as it sought counsel.

“It is illegal for the government to censor the name of Jesus in employee emails,” Jeremy Dys, senior counsel for Liberty Institute, said in a statement. “Censoring a religious club’s announcement to specifically exclude the name ‘Jesus’ is blatant religious discrimination.”