The labor movement unions suffered a major hit to the pocketbook after the U.S. Supreme Court ruled that public sector unions could not force nonmembers to pay dues — and now some of those who had paid for years say they want their money back. Mark Janus, the Illinois state employee who won the Supreme Court case in June, became the latest to demand repayment from the American Federation of State, County and Municipal Employees, for what he estimates is roughly $2,000 in dues he is owed. All told, billions of dollars could be at stake for hundreds of thousands of government workers. But first they will have to prove they’re entitled to collect on the old payments. “It’s quite clear workers can go and get refunds for whatever the statute of limitations is in their state,” said Patrick Semmens, vice president of National Right to Work Legal Defense Foundation, who represented Mr. Janus. Others aren’t so sure, saying the justices didn’t say anything about repayments. “In my view, it’s very unlikely that there will be any retroactivity with respect to this decision, and the reason for that is the Janus decision overruled 41-year-old precedent,” said Mitchell Rubinstein, a New York based lawyer. “It changed existing law.” The high court overturned a 1977 case when it ruled 5-4 in Mr. Janus’ favor. The justices said Mr. Janus was right to complain about being forced to pay dues to a labor union that then used his money to advocate for public policies on education or health care that he disagreed with. The court said the dues were an infringement on Mr. Janus’ free speech rights. Justice Samuel A. Alito Jr., writing for the majority, said losing access to non-members’ money could be “unpleasant” for the unions but Americans’ First Amendment rights needed to be maintained. “It is hard to estimate how many billions of dollars have been taken from nonmembers and transferred to public-sector unions in violation of the First Amendment. Those unconstitutional exactions cannot be allowed to continue indefinitely,” Justice Alito wrote. Even before the ruling, Mr. Semmens‘ organization was battling on behalf of Debora Nearman, an Oregon state employee who objected to her union’s dues. She recently settled with Service Employees International Union (SEIU) Local 503 for roughly $3,000, the amount permitted under the statute of limitations in Oregon for claims brought when civil rights are violated. The National Right to Work Legal Defense Foundation also is representing a class-action lawsuit of more than 30,000 employees in California who are suing the SEIU over its policies, and seeking reimbursement in light of the Supreme Court’s latest ruling. “We actually estimated for them that the over 30,000 workers could be entitled to over a $100 million in refunds,” Mr. Semmens said.