The court announced its decision in a 5-1 vote on Wednesday. Conservative Justice Annette Ziegler was the lone dissenter. Justice Brian Hagedorn, who helped write Act 10 while serving as legal counsel to then-Gov. Scott Walker, did not participate in the decision.

The case arrives at a pivotal moment in Wisconsin politics. Democrats are set to take over the Legislature in January and have signaled support for repealing the law legislatively. The court's decision to hear the union challenge creates a dual-track effort to undo one of the most consequential labor laws in state history.

Act 10, passed in 2011 amid massive protests at the State Capitol, sharply limited the bargaining rights of most public-sector employees, requiring them to contribute more toward pensions and health care and restricting negotiations to base wages. It also ended automatic dues collection for many unions, a change that dramatically reduced union membership and political power across the state.

For years, the law has been a flashpoint in Wisconsin politics, galvanizing labor groups and progressive activists while becoming a model for conservative policymakers nationwide. Unions have argued that the law violates workers' constitutional rights to association and equal protection.

The Supreme Court's decision to take the case means the justices will ultimately decide whether Act 10 survives. A ruling against the law would mark a major victory for organized labor and could restore bargaining rights for tens of thousands of teachers, nurses, and other public employees.

With Democrats poised to control the Legislature, the political landscape has shifted significantly since Act 10 was enacted. The combination of a new legislative majority and a court willing to hear the challenge suggests the law's future is more uncertain than at any point in the past decade.

Oral arguments have not yet been scheduled. The case is expected to draw national attention as a bellwether for labor rights and the power of unions in the Midwest.