The Colorado affiliate of the National Rifle Association sued Boulder on Thursday in an effort to prevent the city from enforcing its assault-weapon ban that takes effect Friday.

Attorneys for the Colorado State Shooting Association, Boulder-based Gunsport of Colorado and two private citizens — James Michael Jones and Robert Lynn Chambers — argue the Boulder ordinance is invalid because sections of it conflict with state law.

The complaint specifically cites three sections of the ordinance that clash with Colorado state statutes. Those are the requirement that owners of banned weapons receive a certificate from the city proving ownership, the prohibition of the sale and possession of weapons by people under 21, and the prohibition on the open carry of rifles and shotguns.

Denver Attorney Richard Westfall, who is representing the plaintiffs, confirmed via email that the suit was filed Thursday. A Boulder spokesman didn’t immediately respond to a request for comment. Gunsport and Jones couldn’t immediately be reached for comment, and when reached by phone on Thursday, Chambers declined to comment.

The NRA voiced support for the lawsuit in a news release. The release did not expressly state that the Colorado association is an official affiliate of the NRA, but included a comment from Anthony Fabian, the state association’s executive director.

“We will not stand by and allow the misguided gun control extremists on the city council to strip us of our rights,” he said. “We are grateful for the NRA’s support of our lawsuit and look forward to restoring the rights of Boulder’s law-abiding citizens.”

The suit comes about a month after another was filed in federal court less than 24 hours after the Boulder City Council unanimously passed the ordinance. The federal lawsuit claims the ordinance violates the plaintiffs’ constitutional rights.

Boulder City Council Member Jill Adler Grano first suggested the ordinance in February after the mass shooting at Marjory Stoneman Douglas High School in Parkland, Fla. left 17 people dead.

Opponents of the ordinance have organized several pro-gun rallies in Boulder and other cities along the Front Range, during which many participants have openly carried weapons that will become illegal in Boulder on Friday.

At a demonstration last week, police passed out pamphlets detailing an existing Boulder ordinance that prohibits the open carry of firearms that aren’t in holsters or some other kind of case but issued no citations.

A violation of the new ordinance could result in sentences of up to 90 days in jail and fines of up to $1,000 — though Boulder officials have acknowledged that it will be difficult to enforce. It bans certain pistols and semi-automatic rifles with pistol grips, a folding or telescoping stock or any protruding grip that allows a weapon to be stabilized with the non-trigger hand.

John Bear: 303-473-1355, bearj@dailycamera.com or twitter.com/johnbearwithme