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AUSTIN (CBSDFW.COM/AP)Texas’ new law allowing concealed handguns in college classrooms and buildings has barely started and already faces a federal legal challenge seeking to block it before students return for the fall semester.

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Three professors at the University of Texas at Austin sued last month to overturn the law. They claimed it is unconstitutional and is forcing colleges to impose “dangerously-experimental gun policies.”

Sociology professor Jennifer Lynn Glass, and English professors Lisa Moore and Mia Carter noted that they each teach emotional topics including abortion, sexuality and gay rights. They say guns in classrooms could disrupt student discussion and violate free speech protections.

The flagship UT Austin campus has been a flashpoint of opposition to the law among faculty and students.

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The Campus Carry law took effect Monday and is in place, in varying degrees, on public universities across the state. The law requires all public universities to allow licensed concealed handguns owners in the classroom, but does give some leeway to schools allowing for gun-free or exclusion zones.

U.S. District Judge Lee Yeakel had previously scheduled a preliminary injunction hearing for Thursday in Austin.

Texas Attorney General Ken Paxton called the lawsuit “frivolous” Tuesday. Gun rights advocates say it’s a key self-defense measure that is protected under the Second Amendment right to bear arms.

Open carry is still banned at private universities and community colleges. Campus Carry laws on those campuses don’t go into effect until 2017.

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