More armed off-duty or retired officers would mitigate a terrorist attack like the one in Paris, the group says.

Chuck Canterbury, the president of the National Fraternal Order of Police, wrote a letter to NFL Commissioner Roger Goodell on November 20 that encouraged him to relax the policy prohibiting firearms at stadiums, claiming it "weakens the safety and security of NFL players, personnel and fans."

"The terrorist attacks and threats of attacks from organizations like the Islamic State of Iraq and the Levant (ISIL) are selecting targets based on the amount of death and injury they can inflict – mass murder and casualty events," the letter reads.

The NFL currently employs off-duty law enforcement officers and private security, as well as metal detectors, for all of its games. "Our procedures have been certified and designated by the Department of Homeland Security since 2008 as effective anti-terrorism technology," the league wrote after the November 13 Paris attacks.