PHOENIX – Favoring the constitutional right to bear arms over others’ concerns about gun safety, Gov. Jan Brewer on Friday signed into law a bill making Arizona the third state allowing people to carry a concealed weapon without requiring a permit.

The measure takes effect 90 days after the current legislative session ends, which likely puts the effective date in July or August.

“I believe this legislation not only protects the Second Amendment rights of Arizona citizens, but restores those rights as well,” Brewer, a Republican, said in a statement.

By eliminating the permit requirement, the Arizona legislation will allow people 21 or older to forego background checks and classes that are now required.

Supporters say the bill promotes constitutional rights and allows people to protect themselves from criminals, while critics worry it will lead to more shootings as people with less training have fewer restrictions on carrying weapons.

Some police officials are concerned the law will lead to more accidental gun discharges from people untrained in firearm safety, or that shooters in stressful situations will accidentally strike innocent bystanders with stray bullets.

“I know a lot of 21-year-olds; the maturity level is gravely concerning sometimes,” said El Mirage Police Chief Mike Frazier, an Arizona Association of Chiefs of Police board member. “If you’re going to be carrying a weapon, you should know what the law is and how to use it.”

However, the measure was supported by police unions representing rank-and-file officers, who said their best friend on the streets is a law-abiding citizen equipped to protect themselves or others.

Democratic Rep. Kyrsten Sinema said the bill deprives law enforcement of a tool “to separate good guys from the bad guys.” With a permit requirement, police encountering a person with a concealed gun but no permit had reason to suspect that person was not a law-abiding citizen, she said.

The Arizona Citizens Defense League, a gun-rights group that lobbied for passage of the “constitutional carry” bill, said gun owners foregoing permits still should get training.

Federal law requires anyone buying a gun from a licensed dealer to undergo a background check, but that requirement does not apply to sales by individuals who aren’t dealers.