The state attorney general's office says the Washington Budget and Policy Center has agreed to pay about $30,000 in relation to violations of state campaign-disclosure law.
The Seattle Times reported Monday that court records show the center didn't properly report independent expenditures it made while opposing Initiative 1366.
Voters in 2015 approved I-1366, a Tim Eyman-sponsored, anti-tax proposal that a court later threw out.
The judgment orders the left-leaning center based in Seattle to pay $33,510 in penalties. Half will be suspended if the center doesn't commit other campaign-finance violations in the next four years.
The center was also ordered to pay nearly $14,000 in attorney fees and other costs.
Officials with the center say the action stems from a complaint filed by the right-leaning Free dom Foundation.