One of Washington’s most politically potent unions could face new obstacles to its organizing clout after a U.S. Supreme Court decision that struck down a similar union’s ability to collect mandatory dues from workers.

In Harris v. Quinn, the court ruled Monday that thousands of Illinois home-health-care workers cannot be forced to pay fees to the Service Employees International Union (SEIU) to cover collective-bargaining expenses.

The court’s 5-4 majority said such mandatory fees violate the free-speech rights of workers who disagree with union political activities.

Labor critics say the decision should apply to some local unions, including SEIU Healthcare 775NW, which represents 35,000 home-health-care workers who contract with the state.

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“I don’t see any reason why the SEIU in Washington would not fall under this ruling,” said Maxford Nelsen, labor-policy analyst for the Freedom Foundation, an Olympia-based conservative think tank.

But state and union officials said they’re still analyzing the decision and were not yet sure of the impacts.

Attorney General Bob Ferguson issued a brief statement saying his office was aware of the decision: “We need time to review it fully and consult with our client agencies to determine what, if any, implications there are for Washington state.”

Jackson Holtz, a spokesman for SEIU Healthcare 775NW, said there are “innumerable” differences between the legal status of Illinois home-health-care workers and those in Washington.

Workers represented by the SEIU here have seen substantial pay and benefit increases, which make “fair share” fees for union representation reasonable, Holtz said.

Holtz added that the SEIU has been “working closely” with the offices of Ferguson and Gov. Jay Inslee in anticipation of the ruling, in case there are “additional steps” the state needs to take “so that the home-care program continues to be strong.”

If Monday’s precedent were to allow SEIU members here to opt out of paying dues, it could threaten the financial underpinnings of the union, which has become a powerful force in state politics, usually aligned with Democrats.

Purple-shirted SEIU activists are a common sight at political rallies, and the union played a key role in pushing through recent minimum-wage increases in Seattle and SeaTac.

But not all home-health-care workers agree with the union’s left-leaning politics or its mandatory fee structure.

Brad Boardman, of Everett, said he’s OK with the union charging for what it costs to represent him and other workers in contract talks.

“But they collect much more than that, and they use that money to further their agenda. I don’t happen to agree with the liberal agenda,” he said.

Boardman, who gets paid to care for his developmentally disabled sister-in-law, said he’s not sure if he’d entirely opt out of union fees if that were allowed.

But he said he’d demand a more detailed explanation on how the SEIU spends the $50 a month deducted from his check.

SEIU Healthcare 775NW collected nearly $20 million in dues in fiscal year 2013, according to filings with the Department of Labor. It spent $2.6 million on political activities and lobbying during that period.

Workers who don’t want to be union members still must pay a lower “agency fee” to help cover the union’s expenses.

In some states, so-called “right to work” laws banning mandatory union dues have hamstrung union finances and organizing efforts.

Monday’s ruling was limited to “partial-public employees” and stopped short of overturning decades of practice that has generally allowed public-sector unions of teachers, firefighters and other government workers to pass through their representation costs to nonmembers.

Writing for the court, Justice Samuel Alito said home-care workers “are different from full-fledged public employees” because they work primarily for their disabled or elderly customers and do not have most of the rights and benefits of state employees.

Some union leaders feared the Supreme Court would issue a much more sweeping ruling, essentially outlawing mandatory dues or fees for all public-sector unions.

That’s still a risk for labor moving forward, as some observers said the court seemed to be inviting further challenges.

But it likely will take a lot more legal wrangling — and likely a local challenge to union dues — before even the impact of Monday’s ruling is known here, said George Lovell, chairman of the political-science department and Harry Bridges Endowed Chair in Labor Studies at the University of Washington.

“It’s a challenge, a new challenge for unions in a difficult time. But they’ve had other challenges before,” Lovell said, adding, “SEIU is a strong union and they have many, many loyal members … so I think they’ll do OK.”

This story contains material from The Associated Press.

Jim Brunner: 206-515-5628 or On Twitter @Jim_Brunner