FILE PHOTO: Trees cast shadows outside the U.S. Supreme Court in Washington, U.S., June 25, 2018. REUTERS/Toya Sarno Jordan/File Photo

WASHINGTON (Reuters) - The U.S. Supreme Court on Wednesday dealt a blow to organized labor, ruling that non-members cannot be forced in certain states to pay fees to unions representing public employees such as teachers and police, shutting off a key union revenue source.

On a 5-4 vote powered by the court’s conservative majority, the justices overturned a 1977 Supreme Court precedent that had allowed the so-called agency fees that are collected from millions of non-union workers in lieu of union dues to fund non-political activities like collective bargaining.

The ruling means that the estimated 5 million non-union workers who pay these fees will no longer have to do so.