The AFL-CIO has filed a lawsuit against the city of Seattle, seeking to overturn a contract that requires unions to pay their dues in full and pay them in full each year.
The lawsuit was filed in U.S. District Court in Seattle.
The city, a union-friendly jurisdiction, says the law violates its constitution and has until Jan. 6 to respond.
The union-led coalition, which represents more than 3 million workers in the Seattle area, said it has received more than $5.4 million in dues from more than 1.3 million workers since the law was passed in February 2014.
The coalition’s lawyers say the law has resulted in higher wages and better working conditions for employees.
The suit comes as Seattle is grappling with a $7.8 billion pension liability, a third of which is due to retiree health benefits.
The unions are also challenging the city’s decision to cut back on services for city employees.
Seattle is one of a handful of cities that has also banned non-essential union activity such as political meetings and other events.