Seattle Seahawks owner Paul Allen watches players warm up before an NFL football game against the Arizona Cardinals, Sunday, Dec. 31, 2017, in Seattle.

Seattle Seahawks owner Paul Allen watches players warm up before an NFL football game against the Arizona Cardinals, Sunday, Dec. 31, 2017, in Seattle.

John Froschauer/AP

Paul Allen, Microsoft co-founder and owner of the Seattle Seahawks and Portland Trail Blazers, has donated $1 million to a campaign seeking to raise the age to purchase semi-automatic rifles from 18 to 21 in Washington state.

Allen made the announcement on Twitter Monday.

The Alliance for Gun Responsibility says Initiative 1639 also would create a background check system similar to the one required for handguns, require completion of a firearms safety course and create standards for safe gun storage.

The group’s initiative effort comes after lawmakers in the Democratic-controlled Statehouse declined to bump the minimum age to buy semi-automatic weapons after the February mass shooting at a Florida high school.

The alliance needs roughly 260,000 petition signatures before the initiative can qualify for the 2018 ballot.

In 2014, Allen donated $500,000 to a successful campaign seeking to expand background checks on gun sales in the state.