The Boulder City Council unanimously passed a sweeping gun control ordinance Tuesday night banning "assault weapons" and bump stocks, even as a pro-Second Amendment group threatened to retaliate by suing individual councilmembers.

In a surprising turn, one Colorado councilwoman admitted that she disagreed with the ordinance "in many ways," saying it would invite a flood of litigation -- despite voting for it.

The city defines assault weapons as "semi-automatic firearms designed with military features to allow rapid spray firing for the quick and efficient killing of humans."

Included in the definition are "all semiautomatic action rifles with a detachable magazine with a capacity of twenty-one or more rounds," as well as "semiautomatic shotguns with a folding stock or a magazine capacity of more than six rounds or both."

"We're going to see a lot of court cases coming before us." — Boulder City Councilwoman Mirabai Nagel

Those possessing assault weapons already can keep them under the law, but owning bump stocks and high-capacity magazines will be become illegal in July. Certain law enforcement and military personnel are exempted from the ordinance.

During the public comment period for the legislation, the nonprofit Mountain States Legal Foundation promised to sue the city for "violations of the Second, Fifth, and Fourteenth Amendments," as well as the Colorado Constitution, Fox's KDVR-TV reported.

RETIRED SUPREME COURT JUSTICE SAYS SECOND AMENDMENT SHOULD BE REPEALED

A staff attorney for the group, Cody Wisniewski, said that individual councilmembers would be named in the lawsuit, according to the network.

Lawsuits generally cannot be directed personally at individual lawmakers for their official actions in legislative sessions, but naming elected officials in civil actions against the government is often acceptable as long as plaintiffs are not seeking to hold lawmakers personally liable for allegedly unconstitutional conduct.

The nonprofit's threat of legal action apparently did not come as a surprise to members of the city council, who said they anticipated complications.

"We're going to see a lot of court cases coming before us," Councilwoman Mirabai Nagle said despite voting for the ordinance, according to Colorado Public Radio. "I think that we're going to spend a lot of time and money. It's not that lives aren't worth that, but I think that there was a better way of going about this.

"I don't agree with this ordinance in many ways," Nagle added. "It's not perfect."

The proposed ordinance led to protests last week, with some pro-Second Amendment activists carrying long guns openly in the streets, according to local reports.

The Boulder City Council tweeted Tuesday that it would soon consider additional amendments to the ordinance, such as raising the age to buy a firearm.

The bill comes after several other state and local governments have passed contentious gun-control measures in the wake of the February mass shooting at a Florida high school.

Amid a barrage of taunts from protesters calling him a "liar" and a "traitor" last month, for example, Vermont Gov. Phil Scott enacted the state's first major gun control measures during a heated signing ceremony at the Statehouse.