A federal judge has denied Maura Healey’s motion to quash testimony from local police departments in a suit by gun retailers over the attorney general’s 2016 crackdown on so-called copycat assault weapons.

The attorney general issued the notice in July 2016, warning her office would increase enforcement of the state’s assault weapons ban and crack down on copycat weapons which would be identified using two tests. Business owners argue the notice is unconstitutionally vague, violates the Second Amendment and deprives gun shops of property without due process.

Federal Magistrate Judge David Hennessy wrote in a motion ruling Tuesday that information from the Holyoke, Worcester, Orange and Agawam police departments was relevant to the case. Healey objected to their testimony because it sought discovery on matters beyond the scope of the claims, she said, and placed an undue burden on the departments.

Hennessy wrote the police departments’ testimony was relevant because of Healey’s own admission in filings that “the AG is not the only law enforcement officer” authorized to enforce the state’s assault weapons ban.

The plaintiffs have also served subpoenas for the state police, the Massachusetts Executive Office of Public Safety and Security and Gov. Charlie Baker’s office.

Attorneys for the gun shops argued in an opposition to Healey’s motion that the enforcement notice wasn’t clear because the attorney general took over two years to figure out how to apply two tests to determine if guns were copies or duplicates of banned assault weapons. They also questioned Healey’s assertion that the distinction between banned and allowed weapons “has always been clear to persons of ordinary intelligence.”

“For the Attorney General to state that …” the attorneys wrote, “… necessarily implies that those people from the Attorney General’s Office who struggled and were unable to determine its meaning … must not be of ordinary intelligence.”

A federal judge ruled in March 2018 against Healey’s bid to dismiss the suit, saying the business owners’ case had merit. The gun shops’ amended complaint concerns the application of the enforcement notice to seven weapons including .22 caliber rimfire AR-15 style rifles.