The high court ruled the restrictions covering labor unions for public employees do not violate the union's constitutional free-speech rights to engage in political advocacy.
Washington voters in 1992 adopted a campaign finance law that required unions to get the consent of each worker before spending fees on political activity, such as campaigning for or against various measures.
The law also required the unions to refund the fee to nonmembers who oppose the political activity proposed by the union.
The case involved the Washington Education Association, the state's largest teachers union. About 4,000 of the more than 70,000 people it represents choose not to be members, according to the union, which said Washington is the only state in the nation with such a law.
Lawyers for the state and the Bush administration urged the Supreme Court to uphold the law because it was designed to regulate campaign financing in state elections. The high court agreed in an opinion written by Justice Antonin Scalia.
"The purpose of the voters of Washington was undoubtedly the general one of protecting the integrity of elections by limiting electoral spending in certain ways," Scalia said.
"Quite obviously, no suppression of ideas is afoot, since the union remains as free as any other entity to participate in the electoral process with all available funds other than" those fees by nonmembers who refuse to give their approval, Scalia said.
