A public university in Colorado was sued by the Alliance Defending Freedom (ADF), a conservative Christian nonprofit organisation, after it prohibited a former football player from putting Bible verses on a donor nameplate.

The ADF filed the lawsuit against the Colorado School of Mines (CSM) on Wednesday after alumnus Michael Lucas was refused by the school to include the inscription "Colossians 3:23 and Micah 5:9" on a nameplate that will be put in a new football locker room, an ADF press statement said.

The school allows donors to its athletic facility to include any inscription on personalised nameplates. But it said it rejected Lucas' inscription because one of the verses refers to "Lord" even though the text of the verses would not appear on the nameplate itself.

"Public colleges and universities should encourage, not shut down, the free exchange of ideas, especially in a forum like this. The school initially imposed no restrictions—or even guidelines—on the type of message a donor could include, and contrary to what the school is arguing, the First Amendment protects—not restricts—a simple reference to a Bible verse," said ADF legal counsel Natalie Decker.

Decker said, "it's patently ridiculous to argue that a Bible reference that doesn't include the text of the verse is somehow inappropriate simply because someone might look it up and see that 'Lord' is mentioned there."

Lucas graduated from CSM in 2003 and joined the school's fundraising programme for the new Clear Creek Athletics Complex.

Each nameplate could include three lines of a personalised message or a quote chosen by the donor.

CSM approved other nameplate inscriptions including "Give 'Em Hell," "OK Gentlemen, it's time to gird your loins," and "Take your whiskey clear."

"The United States Constitution prohibits the government from treating religion with hostility or from excessively entangling the government with religion," according to the lawsuit. "The censorship of Mr. Lucas' religious speech—while permitting similar, but nonreligious, private speech from other members of the public regarding the same and similar subject matters—also constitutes viewpoint discrimination, which is unconstitutional in any type of forum."

"Public colleges are supposed to be a marketplace of ideas," said ADF Senior Counsel Tyson Langhofer. "We hope CSM will end the need for this lawsuit and revise its policy so that it affirms the constitutionally protected freedoms of all alumni, regardless of their religious beliefs."