Voters approved new gun regulations in I-1639. Here’s what the law will do.

OLYMPIA — Washington voters approved a sweeping package of gun regulations Tuesday, the latest in a handful of firearms-related initiatives in recent years. Initiative 1639 passed with more than 60 percent of the vote. Opponents say they will sue in an attempt to block the law.

Here’s a quick recap of the initiative.

Q: What does the initiative do?

A: I-1639 raises the legal age to buy any semi-automatic rifle to 21, from 18. People wanting one also have to pass an enhanced background check, show proof that they have taken a firearms-training course, and wait 10 business days before they take possession of the weapon.

The initiative defines a semi-automatic rifle as one that uses energy from firing a cartridge to chamber the next round and requires “a separate pull of the trigger” to fire each bullet. Long guns that use manual operations — such as pumps, slides, levers or bolts — to chamber a round would still be available for people to purchase at age 18. (You currently have to be 21 to buy a handgun in Washington.)

The initiative allows the state to require firearms dealers to charge up to $25 to purchasers of a semi-automatic rifle to offset the costs of complying with the regulations. That fee could go up over time.

And the initiative directs the state to begin developing a process to check at least annually to make sure owners of handguns and semi-automatic rifles are still legally eligible to possess them.

Q: What about the “safe storage” provision?

A: That’s the other big part of I-1639. The initiative creates gross-misdemeanor and felony classes of a new crime, “community endangerment.”

It doesn’t mandate that firearms owners lock their guns away. But owners could be charged under those community-endangerment crimes if someone not allowed to access a firearm — such as a child or a felon — gets ahold of it and displays it publicly, causes it to discharge or uses it in a crime.

Owners who keep a gun secured in a safe or lock box, or with a trigger lock or similar device, would not be subject to charges if the firearm is somehow accessed by someone who shouldn’t have it. The community-endangerment charges also don’t apply if a prohibited person obtains a gun due to unlawful entry, as long as the gun owner reports the incident within five days of the time he or she knew or should have known it occurred.

At least 16 states have some kind of criminal liability for a gun owner if a firearm is improperly stored and a child uses or carries it. Eleven states have laws that either encourage or require trigger-lock or secure storage devices for guns.

Q. When does the law go into effect?

A. The initiative says the provision that raises the minimum age to legally purchase a semi-automatic rifles to 21 will take effect Jan. 1. The rest of the provisions go into effect July 1.

Q. Who was behind this initiative?

A. This was the third in a series of ballot measures brought by the Alliance for Gun Responsibility in recent years in response to the mass shootings that have occurred nationwide, as well as other, less publicized firearms-related deaths and injuries.

I-1639’s citizen sponsor was Paul Kramer, the father of a teenager injured in a 2016 Mukilteo house-party shooting that left three others dead. The shooter in that instance was a 19-year-old who bought an AR-15 rifle about a week before the attack.

The “yes” campaign raised nearly $5.5 million, with much of that coming from a handful of big-dollar donors, like venture capitalist Nick Hanauer, former Microsoft CEO Steve Ballmer and Microsoft co-founder and philanthropist Paul Allen, who died last month.

Supporters of the initiative included two of King County’s top law-enforcement officials, Prosecutor Dan Satterberg and Sheriff Mitzi Johanknecht, as well as state Attorney General Bob Ferguson.

Q. Who were the opponents?

A. The largest opposition groups were the National Rifle Association and a pair of Bellevue-based gun-rights organizations, the Second Amendment Foundation and Citizens Committee for the Right to Keep and Bear Arms. Those groups raised roughly $610,000 in cash and in-kind donations to fight the measure, campaign-finance records show.

Several Washington law-enforcement groups or their members also opposed the initiative.

Q: What were the opponents’ arguments?

A: Gun-rights supporters called I-1639 poorly written and likely ineffective. They also argued it would criminalize self defense by allowing charges against a gun owner whose firearm unintentionally falls into the wrong hands.

Others say the initiative unfairly lumps some guns into its restrictions, such as types of .22-caliber hunting rifles that are not comparable to the AR-15 assault-style weapons that draw attention in mass shootings.

Some law-enforcement groups contended I-1639 could be unconstitutional and does nothing to address gun violence related to mental health or substance abuse. Others objected that the initiative doesn’t exempt police officers from its provisions.

Some members of the Washington state Fraternal Order of Police said the initiative would stigmatize the semi-automatic rifles used by officers, since the initiative language refers to them as “assault” rifles, said Lynnette Buffington, executive director of the group.

Gun-rights supporters also contended the initiative’s petition sheets were unlawfully formatted, because they did not show exactly how the measure would change existing state law.

A Thurston County judge agreed with that argument and blocked the initiative — but the Washington state Supreme Court later weighed in and put I-1639 back on the ballot.

Alan Gottlieb of the Second Amendment Foundation and Citizens Committee for the Right to Keep and Bear Arms said Tuesday night, after the initiative passed, that it would be challenged in court. Gottlieb declined to explain the grounds for any challenge.