SEATTLE (AP) — Washington on Tuesday joined a handful of other states that ban anyone under 21 from buying a semi-automatic rifle after voters passed a sweeping firearms measure in November.

The ballot initiative seeks to curb gun violence by toughening background checks, increasing the age limit to buy those firearms and requiring the safe storage of all guns. Only the age-limit portion of the measure went into effect on Jan. 1; the rest becomes law on July 1.

Fifty-nine percent of Washington voters approved Initiative 1639 in the Nov. 6 general election. Opponents, including firearms dealers, the Second Amendment Foundation and the NRA, have sued to block it.