Gov. Maura Healey officially declared a gun reform bill she signed into law more than two months ago an emergency measure Wednesday afternoon, arguing the statute is necessary to preserve the “public peace, health, safety and convenience” of residents in the state.

Her signature means many provisions in the 100-plus page bill took effect immediately rather than later in October. But even as some advocates celebrated the move, Second Amendment rights groups saw their effort to immediately suspend the measure for two years by collecting nearly 50,000 voter signatures crumble under Healey’s executive authority.

At an unrelated event in Framingham, Healey pushed back on criticism from gun groups that she declared the law an emergency only to beat back the attempt to shelve its implementation until the 2026 elections, when voters could be asked to repeal the statute.

“This is about ensuring that we’re ready to go in terms of implementation. The system is there. It’s a democracy. You can go to your Legislature and you can advocate for policy and advocate for laws, and that’s the way the system works,” she said.

A day after Healey’s intention to use her executive authority to put the law into effect immediately became public, she sent a letter to Secretary of State William Galvin making the decision official.

In the message to Galvin, Healey outlined many of the provisions of the law, including how it takes aim at untraceable “ghost guns” and 3-D printed guns, enhances so-called Red Flag laws, and updates the state’s assault weapons ban.

“Strong gun laws save lives,” Healey wrote in the letter. “This law is the state’s most significant gun safety legislation in a decade. It will make Massachusetts safer as soon as it goes into effect, including by keeping assault-style weapons that are a danger to our communities off our streets, and by keeping guns out of government buildings and courts.”

Healey said officials will begin implementing portions of the bill Wednesday, including provisions that govern inspections of firearms dealers, establishment of a new firearms control advisory board, and notifications related to applications for civil commitments and the expiration of harassment prevention orders.

The law also bans people under 21 from owning semiautomatic rifles or shotguns and bars technology that turns semiautomatic firearms into fully automatic ones.

Other portions of the bill also put in place a series of new training and licensing requirements, but lawmakers on Beacon Hill last month used a separate budget bill to push back their effective dates, a move they said they took after discovering a drafting error in the law.

Healey has the authority to declare laws an emergency through the state’s constitution either as she signs the bill or after. Lawmakers can also attach emergency language to bills prior to their final passage.

Gun groups — which can still collect more than 37,000 signatures to put a question before voters in 2026 asking them to repeal the law — have slammed Healey’s decision.

Toby Leary, owner of Cape Gun Works and the head of a coalition that was leading the effort to suspend and repeal the law, said if Healey “truly” thought there was a public health emergency, she would have declared the law an emergency when she signed it in late July.

“She’s acting more like a dictator than a governor. As a store owner, I’m faced with two choices — break the law to stay open or stop selling guns and close my business. After a decade of hard work, my state government is trying to destroy my business’s future,” Leary said in a statement.