Opponents of a bill to allow firearms on Georgia's public college and university campuses have upped their campaign urging Gov. Nathan Deal to reject the measure, releasing a letter Monday in which they try to lay out arguments bolstering Deal's veto of a similar measure last year.

The sponsor of House Bill 280, state Rep. Mandi Ballinger, R-Canton, has repeatedly made the argument that students have a right to protect themselves in a legal manner on campus just as they can off it. She said the bill only applies to students 21 years and older who receive permission to have a concealed carry permit in Georgia. To get the permit, they are required to be fingerprinted and pass a background check. The bill additionally exempts some areas from weapons, including dormitories, sorority and fraternity houses, athletic events and on-campus child care centers.

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But the New York-based Campaign to Keep Guns Off Campus in its letter argues that the Second Amendment has not historically protected carrying concealed weapons on campus. The group, which sent the letter privately to Deal earlier this month, also cited studies saying there is little data to show allowing concealed weapons makes students safer. And they reviewed efforts by both the state’s University System and Technical College System to increase campus security measures, something Deal called for last year.

A Senate committee last week added an additional exemption to the bill for areas on some campuses where high schoolers attend class, a change that keeps it alive as lawmakers continue to negotiate with Deal. The bill is currently in the Senate Rules Committee, which decides which bills receive a vote in the chamber.

Deal has said he would prefer additional exemptions to the bill that include faculty and administrative office space as well as disciplinary hearings.