A divided U.S. Supreme Court said government employees have a constitutional right not to pay union fees in a ruling that affects 5 million workers and deals a heavy blow to the labor movement.

The 5-4 decision overturns a 1977 Supreme Court ruling that had let public-sector unions collect so-called agency fees from non-members to help cover the cost of collective bargaining. The court’s newest member, Neil Gorsuch, joined his conservative colleagues in the majority.

Writing for the court, Justice Samuel Alito said mandatory fees violated the free speech rights of workers who disagree with the union’s positions.

“The idea of public-sector unionization and agency fees would astound those who framed and ratified the Bill of Rights,” Alito wrote.

The case split the court along ideological lines. Justices Ruth Bader Ginsburg, Elena Kagan, Stephen Breyer and Sonia Sotomayor dissented.

“There is no sugarcoating today’s opinion,” Kagan wrote for the group. “The majority overthrows a decision entrenched in this nation’s law — and in its economic life — for over 40 years. As a result, it prevents the American people, acting through their state and local officials, from making important choices about workplace governance.”

President Donald Trump, on Twitter, called the ruling a “Big loss for the coffers of the Democrats!”

Scalia’s Death

The ruling was years in the making for right-to-work advocates and the court’s conservative wing. In 2016 the court had appeared poised to overturn the 1977 ruling, but Justice Antonin Scalia’s unexpected death left the conservatives one vote short.

The 1977 ruling, Abood v. Detroit Board of Education, said states could let public-sector unions demand agency fees, as long as the money covered representational work like collective bargaining and not ideological or political activities like lobbying.

The Abood court said agency fees could promote “labor peace” by buttressing a union’s status as the exclusive representative of a workforce.

The clash was as much about the value of unions as it is about constitutional rights. Union leaders said the ultimate goal of those pressing the case was to undermine the clout of the labor movement. Agency fees had been legal in about two dozen states.

Public-sector unions could now see their ranks shrink. The nonprofit Illinois Economic Policy Institute estimated before the ruling that membership among state and local government employees would decline by 8 percent, while others say the number is likely to be higher. Unionization levels in states with right-to-work laws have been less than half what they are in the rest of the country.

Right-to-work groups, backed by the Trump administration, contended that public-sector unions are engaging in political speech when they negotiate with the government. The groups said workers have a constitutional right not to associate themselves with that speech.

Supporters of agency fees said they ensure employees don’t become “free riders,” benefiting from collective bargaining without paying for it.

The case is Janus v. American Federation of State, County and Municipal Employees, Council 31, 16-1466.