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.

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“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.

The restrictions are prompting a boom in sales for gun shop owners across the state.

“We're probably up by 400 percent from where we were last year for this past month, and this month, in total sales,” Kash said.

Under the new law, all ammo sales must take place in person, even if the initial purchase was made online, individuals will have to come in and pick up the ammo in-store.

If a gun owner is already in the state’s registry and cleared with a background check, they will only pay a $1 processing fee each time they go to buy ammo to run the background check as a “spot check” to ensure there are no new criminal convictions or mental health red flags.

The law was championed by Gov. Gavin Newsom Gavin NewsomOVERNIGHT ENERGY: California seeks to sell only electric cars by 2035 | EPA threatens to close New York City office after Trump threats to 'anarchist' cities | House energy package sparks criticism from left and right California seeks to sell only electric cars by 2035 EPA head questions connection of climate change to natural disasters MORE (D), an outspoken advocate for gun control. He said cracking down on ammo sales will help limit gun crimes in the state.

“A gun requires a dangerous component and that’s ammunition,” he said last week before the law took effect.