Gun owners in California are stocking up on ammunition as the state’s new law requiring background checks to purchase ammo takes effect.

The new law, which goes into effect Monday, makes California the first state in the country to require background checks for ammo purchases. In the week ahead of the law’s implementation, gun owners were flocking to stores to buy ammo, according to USA Today.

“Everybody that has a gun … knows about the law that’s upcoming,” Daniel Kash, LAX Ammunition president, told the news outlet. “People are stocking up right now, basically.”

Proposition 63, the gun control measure placing restrictions on ammo purchases, was overwhelmingly passed by California voters in 2016 but is only now going into effect because of the implementation language in the measure.