Microsoft CEO Steve Ballmer responds to a shareholder question during the Microsoft Shareholders Annual Meeting in 2013 in Bellevue, Wash. (Stephen Brashear/Getty Images)

Former Microsoft CEO and newly named Los Angeles Clippers owner Steve Ballmer and his wife, Connie, have donated $575,000 to a group supporting a Washington state ballot measure that would require universal background checks for gun buyers.

Their donations, in addition to $385,000 from venture capitalist Nicholas Hanauer and $50,000 from Bill and Melinda Gates, add to a $3.3 million war chest raised by the Washington Alliance for Gun Responsibility. The group is seeking to pass Initiative 594, which would require all gun buyers to go through background checks regardless of where they purchase the gun.

Currently, background checks are only required for purchases made through licensed gun dealers, but not through independent sellers, the Internet or through exchanges made at gun shows. If passed, the measure would require anyone buying a gun to receive a background check from a licensed dealer; there are 1,100 such dealers in the state.

Geoff Potter, the communications director for the Washington Alliance for Gun Responsibility, said the group is grateful to the Ballmers and the others for their donations, and he stressed there was broad support for the measure.

“We have now 7,100 donors to the campaign from virtually every county,” he said. “The median donation is $50.”

h/t The Seattle Times