A coalition of gun rights groups is suing Maine over a law requiring a three-day waiting period to buy a firearm, arguing that the new requirements violate the Constitution.

The lawsuit, filed in U.S. District Court in Maine by The Sportsman’s Alliance of Maine, Gun Owners of Maine, and other groups, alleges that the law requiring people to wait 72 hours to acquire a firearm—even if they pass a criminal background check—is an "unadorned effort to delay the exercise of Second Amendment rights" that should be overturned by the court.

"There is no long-standing tradition in this country of forcing law-abiding citizens to wait to acquire firearms," lawyers for the plaintiffs wrote in the 26-page federal court complaint. "While some states adopted waiting-period laws in the early- and mid- twentieth-century, those laws were imposed to facilitate background checks or other investigatory efforts to determine whether someone is prohibited from possessing a firearm."

The 72-hour "cooling off" period was a provision of a broader gun-control bill Democratic lawmakers through the House and Senate in response to the Oct. 25, 2023 Lewiston massacre, when an Army reservist opened fire in a bowling alley and bar in Lewiston, killing 13 people and injuring 18 others. Republicans argued the rules would do little to prevent gun violence and accused Democrats of using the Lewiston shooting for political gain.

Gov. Janet Mills, a Democrat, allowed the 72-hour waiting period to become law without her signature, saying she was "conflicted" over the measure after considering both sides of the gun control debate.

The National Rifle Association blasted Mills for approving the package of bills it says will "destroy Maine hunting tourism, and block the ability for domestic abuse survivors the ability to arm and protect themselves."

The plaintiffs in the lawsuit are being represented by the law firm of Clement & Murphy, which represented the challengers in the U.S. Supreme Court's landmark ruling in the New York State Rifle and Pistol Association v. Bruen case, which struck down a New York law requiring applicants to show "proper cause" to get a permit to carry a firearm.

"Responsible gun owners should never have to wait to exercise the right to defend themselves and their property, and the 72-Hour waiting period law is an affront to that right the likes of which has never been seen in our state," the coalition said in a statement on its website.

Maine's Attorney General Aaron Frey said his office is prepared to defend the law in court, arguing that waiting periods can help prevent impulsive decisions that can lead to mass shootings.

"We look forward to defending this important public safety law," Frey, a Democrat, said in a statement. "Waiting periods have been upheld across the country as a reasonable, limited regulation that does not infringe on Second Amendment rights."