Sparked by last year's mass shooting in Las Vegas, Washington is the most recent state to ban trigger devices that allow semi-automatic rifles to fire more rapidly.
Gov. Jay Inslee signed the ban into law Tuesday.
Washington was among more than 20 states that introduced legislation seeking to ban the devices, known as bump stocks, after the Oct. 1 attack that was the deadliest mass shooting in recent U.S. history.
Washington now joins Massachusetts, New Jersey and the cities of Denver and Columbia, South Carolina, in banning bump stocks since the Las Vegas shooting, according to the National Conference of State Legislatures.
The new law makes it illegal for anyone in Washington to manufacture or sell bump stocks beginning July 1. In July 2019, it would become illegal to own or possess a bump stock in the state.