Washington voters passed Initiative 1639, which would make the state’s gun laws some of the strictest in the nation, in Tuesday night’s count.

The “Safe Schools, Safe Communities” initiative passed statewide with 60.4 percent voting yes and 39.65 percent voting no as of Tuesday night. In Whitman County, the initiative faced a much closer margin with 50.65 percent voting yes and 49.35 opposing.

The initiative seeks to address the root causes of mass shootings through “common sense” regulation, according to the Yes on 1639 campaign website.

The measure will raise the purchasing age of semi-automatic rifles from 18 to 21, a restriction already in place for the purchase of handguns.

In order to buy a semi-automatic rifle, a potential owner will be required to pass an enhanced background check, have taken a gun safety and training course within five years of the purchase and go through a 10-day waiting period, according to the Washington Secretary of State website.

Another function of the measure is to encourage the secure storage of firearms. Gun owners could face criminal prosecution if a prohibited person gains access to a weapon that was not responsibly stored and uses it in a crime, according to the website.

Before the initiative was passed, the Giffords Law Center, a national organization dedicated to preventing gun violence in the U.S., ranked Washington 10th in the nation for strongest gun laws.

The initiative was backed by high-profile donors such as the late co-founder of Microsoft Paul Allen, according to The Seattle Times. It was also the only gun regulation initiative on the ballot in the state.

Of the 6,377 votes counted in Whitman county Tuesday night, 3,230 voted in favor and 3,147 voted against, a difference of only 83 votes.