(Adds comments from DCCC, conservatives)
WASHINGTON, June 27 (Reuters) - A U.S. Supreme Court decision on Wednesday limiting public sector labor unions' ability to collect fees from employees could reduce the cash that unions can pump into Democratic campaigns for congressional elections in November.
The ruling that non-members cannot be forced in certain states to pay fees to unions representing public employees such as teachers and police, limits an important union revenue source.
"In the short run, it will starve resources," said Stephen Silvia, an American University economics professor who studies unions. "The amount of resources that go to Democratic candidates is likely to decline as a result of this decision."
Silvia said the change would not affect just unions' ability to cut checks for candidates or to purchase expensive television advertisements. Grassroots efforts, such as organizing phone banks and voter turnout programs, also require resources.
The Supreme Court decision may let unions be more overtly political because they no longer will represent paying members who have opted out of the union, Silvia said.
In the 2016 election cycle, unions collectively spent more than $160 million. Some was given to so-called super PACs that can spend and raise unlimited sums and a portion went to fund internal union political operations.
The impact of Wednesday's decision may be blunted because several unions expected to lose the case and already had started to adjust their electoral strategies. For some, that meant dropping messages targeted at the general public and redirecting attention toward their own membership, said John Weber, spokesman for the AFL-CIO, a confederation of labor unions.
"We'll be the first to say we didn't do things right in 2016," Weber said. "We looked in the mirror and recalibrated."
Last week, the AFL-CIO began an effort centered on the congressional elections meant to encourage more internal union discussions on politics.
People trust their own union and local members, Weber said, and that makes them the most reliable source when discussing elections.
He pointed to the Pennsylvania special election won by Democrat Conor Lamb in which Republicans drastically outspent their opponents but union members across the Pittsburgh-area district rallied to push Lamb to victory.
The committee tasked with electing Democrats to Congress painted the ruling as purely political.
"Attacking unions and the hard-working people who make up Americas workforce has long defined the Republican Partys backwards agenda, said Tyler Law, spokesman for the Democratic Congressional Campaign Committee.
Sue Schurman, a business professor at Rutgers University who specializes in unions, said the court's decision might not cripple Democrats in the way Republicans had hoped. "Grassroots organizing doesn't take a lot of resources in today's world," she said. "Social media has made it much easier for constituencies to mobilize and express their political clout."
Conservative cheered the decision.
"Collective bargaining with the government directly impacts public policy so these mandatory dues represent forced political speech," said Nathan Nascimento, the head of policy for the Freedom Partners, the group backed by the Koch brothers who have aggressively back Republican candidates. (Reporting by Ginger Gibson Editing by Kevin Drawbaugh, Grant McCool and Bill Trott)