Washington state on Tuesday officially banned anyone under age 21 from buying semi-automatic assault rifles.

The ballot initiative, which passed with 59 percent support of voters in November, sought to implement a series of gun control reforms, The Associated Press reported.

The ballot initiative aims to limit gun violence by strengthening background checks for those buying assault rifles, upping the age limit to purchase such firearms and requiring safe storage for all guns. The age restrictions for semi-automatic assault rifles was implemented on Jan. 1., but the rest of the measure's requirements take effect on July 1.

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Washington residents will now have to pass through FBI's National Instant Criminal Background Check System before purchasing long guns.

Kristen Ellingboe, a spokeswoman for the Washington Alliance for Gun Responsibility, told the outlet that Washington’s new firearms legislation is one of the most comprehensive in the country.

"We've seen that assault rifles are the weapon of choice for mass shootings, and when they're used, more people are killed and injured," Ellingboe said.

Florida passed similar legislations on semi-automatic assault rifles after a gunman killed 17 people inside Marjory Stoneman Douglas High School in Parkland, Fla., last February.

Four other states — Hawaii, Illinois, Vermont and New York — have banned the sale of firearms to those under 21.

Gun rights advocates and the National Rifle Association (NRA) argue that the age restrictions violate the constitutional rights of people between the ages of 18 and 20.

“We need serious proposals to prevent violent criminals and the dangerously mentally ill from acquiring firearms,” NRA spokeswoman Jennifer Baker said in a statement after the mass shooting.

“Passing a law that makes it illegal for a 20-year-old to purchase a shotgun for hunting or adult single mother from purchasing the most effective self-defense rifle on the market punishes law-abiding citizens for the evil acts of criminals,” she added.

A federal lawsuit was filed by firearms dealers, a 19-year-old competitive shooter, a 19-year-old in the Army Reserves, a 20-year-old recreational shooter, the Second Amendment Foundation and the NRA to block the legislation, the AP reported.

Washington Attorney General Bob Ferguson told the outlet that he is looking forward to facing off against the NRA in court.

"The gun lobby is trying to thwart the will of nearly 60 percent of Washingtonian voters who supported common sense gun reform in our state," he said.