By Jon Herskovitz

AUSTIN, Texas (Reuters) - Three University of Texas professors asked a U.S. judge on Thursday to give them the option of barring students from bringing guns into their classroom after the state gave some students that right under a law then went into effect this week.

The professors said academic freedom could be chilled under the so-called campus carry law backed by the state's Republican political leaders that allows concealed handgun license holders 21 and over to bring handguns into classrooms and other university facilities.

"They don't fear, they know that the presence of guns in their classrooms... would squelch (academic) discussions," Renea Hicks, a lawyer for the professors told U.S. District Judge Lee Yeakel.

The lawsuit is seeking a preliminary injunction to halt guns in the classrooms of professors Jennifer Lynn Glass, Lisa Moore and Mia Carter ahead of the start of classes later this month.

Anna Mackin, an attorney for the university, told the judge that if the professors banned guns in their classroom, they would be violating state law, and could be disciplined or terminated.

Texas Attorney General Ken Paxton, a Republican and a defendant in the suit, filed papers to halt the injunction, calling the professors' case a "frivolous lawsuit."

"There is no legal justification to deny licensed, law-abiding citizens on campus the same measure of personal protection they are entitled to elsewhere in Texas," Paxton said in a statement this week.

Lawyers for the professors said they expect a decision before Aug. 24.

The professors argue they discus emotionally laden subjects such as reproductive rights, and it would be inevitable for them to alter their classroom presentations because of potential gun violence.

The law took effect on Aug. 1 as the University of Texas held a memorial to mark the 50th anniversary of one of the deadliest U.S. gun incidents on a college campus.

On Aug. 1 1966, student Charles Whitman killed 16 people in a rampage, firing from a perch atop the clock tower at the University of Texas at Austin, the state's flagship public university.

Republican lawmakers said campus carry could help prevent a mass shooting.

University of Texas professors lobbied unsuccessfully to prevent the campus carry law, arguing the combination of youth, firearms and college life could make for a deadly situation.

Eight states have provisions allowing the carrying of concealed weapons on public postsecondary campuses, according to the National Conference of State Legislatures, which tracks state laws.

(Reporting by Jon Herskovitz; Editing by Sandra Maler)