A Wisconsin judge on Monday struck down portions of a 2011 law that stripped most government workers in the state of collective bargaining rights and set off fierce demonstrations.

The ruling by Judge Jacob Frost of the Dane County Circuit Court is certain to be appealed. But his decision provided at least a temporary victory to labor unions and Democrats in Wisconsin, who turned out by the thousands to protest the law more than a decade ago and who have been trying ever since to take it off the books.

Republicans passed the law, known as Act 10, shortly after winning control of state government in the 2010 elections, arguing that limits on public sector unions were necessary to balance the budget and attract business investments. They advanced the legislation despite large-scale protests at the State Capitol in Madison and an attempt by Democratic lawmakers to scuttle the vote by fleeing to Illinois.

Robin Vos, the Republican speaker of the Wisconsin Assembly, vowed in a statement on Monday to appeal the ruling.

“This lawsuit came more than a decade after Act 10 became law and after many courts rejected the same meritless legal challenges,” Mr. Vos said.

The case seems likely to end up before the Wisconsin Supreme Court, which has been at the center of recent battles over elections and abortion.

That court is officially nonpartisan but has grown highly politicized. Liberals currently hold a one-seat majority, but conservatives would regain control if their candidate wins a spring election for an open seat.

Thirteen years after the Act 10 protests, Wisconsin remains closely divided. President-elect Donald J. Trump narrowly carried the state last month, while voters also elected Senator Tammy Baldwin, a Democrat, to another term.