Hundreds of Bay State gun owners rallied outside the State House yesterday to protest Attorney General Maura Healey’s push to ban so-called “copycat” assault rifles — a move that many demonstrators said has turned them into felons overnight.

“I can’t believe that the attorney general feels she has the power to use her pen to trample on the rights of citizens of Massachusetts while the Legislature is out of session,” said Kristina Sears of Easthampton. “There was no warning, no discussion, no anything.”

Chanting “Healey for harbor” as passing motorists honked in support, a throng of gun rights activists from across the state waved flags and held up handmade signs to demand due process and consideration for their rights.

Activists waving American Revolution-era “Don’t Tread on Me” flags and American flags were flanked by protesters with signs reading “Baker betrayed us,” “Overnight Felon,” and “2nd amendment or 2nd class citizens.”

Many of the gun owners gathered on Beacon Street yesterday told the Herald they have been “sick” since Healey announced her plan to step up enforcement of the state’s assault weapons ban on Wednesday.

Healey’s office contends that the state assault weapons ban mirrors the federal ban that expired in 2004. Her office argues the law prohibits sales of specific weapons and bans duplicates of those weapons, but gun manufacturers have made minor tweaks to various parts of the weapons to make them state compliant.

A number of gun owners at the Boston rally said they have owned copies of the Colt AR-15 and Kalishnikov AK-47 for a long time.

Protesters argued that Healey’s plan will punish law-abiding citizens and infringe on their Second Amendment rights. Many wondered how they will be protected from prosecution if they legally purchased copycats that are now banned under Healey’s order.

“I think it’s garbage,” said Justin Coletti of Peabody. “If you can easily interpret the law without due process, imagine what other laws will be gone.”

Healey’s office has said it won’t prosecute people who purchased the guns by the end of business Wednesday. But that wasn’t enough, protesters said.

“This law has been interpreted the same way for decades,” said James Conner-Myers of Methuen. “All of a sudden I wake up and I’m told I’ve committed a felony.”