WASHINGTON, June 21 (Reuters) - The U.S. Supreme Court ruled on Thursday that free-speech rights require that a union provide a separate notice allowing nonmembers to object before imposing a special extra fee to raise funds for political or other purposes.

By a 7-2 vote, the justices ruled for a group of California workers who sued to stop the 2.1-million-member Service Employees International Union from collecting extra money from those nonmembers who did not want to pay the fee.

The majority opinion written by Justice Samuel Alito cited the free-speech rights under the Constitution's First Amendment and said there was no justification for the union's failure to provide a new notice for nonmembers.

When a public-sector union imposes a special assessment or dues increase to meet expenses not previously disclosed, it must provide a new notice and cannot collect any funds from nonmembers without their approval, he said.

The ruling was the latest in a series by the court in recent years that have gone against the unions on the fees used to finance political or other activities that some workers oppose. The court previously held workers must be given the chance to opt out of the fees.

The Service Employees International Union is the exclusive bargaining representative for California state employees. It issued a special midyear fee assessment in 2005 to members and nonmembers to raise funds to oppose ballot initiatives and for bargaining-related and other purposes.

The union did not provide nonmembers with a separate, distinct notice and opportunity to object to the assessment, as it did with its regular annual fee assessments.

The workers argued in their class-action lawsuit on behalf of 28,000 nonunion employees that their free-speech and due process rights had been violated. At stake was about $12 million.

A U.S. appeals court ruled for the union, holding the special assessment satisfied all procedural requirements and did not violate the workers' free-speech rights.

The Supreme Court overturned that decision. "The general rule - individuals should not be compelled to subsidize private groups or speech - should prevail," Alito wrote.

Justices Stephen Breyer and Elena Kagan dissented. Breyer wrote that the special assessment as administered by the union imposed no constitutional harm on the nonmembers.

The Supreme Court case is Knox v. Service Employees International Union, No. 10-1121.

For Knox: James Young of the National Right to Work Legal Defense Foundation.

For Service Employees International Union: Jeffrey Demain of Altshuler Berzon.

(Reporting by James Vicini)

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