Gig workers and labor unions on Thursday continued their challenge to California’s Proposition 22, filing a lawsuit in a lower court as urged by the state Supreme Court, which last week rejected a request for an expedited review of the case.

The plaintiffs, who filed the lawsuit in January, say the measure, which 58% of the state’s voters passed in November and exempts companies like Uber Technologies Inc. and Lyft Inc. from a law that would require them to treat their drivers as employees, is unconstitutional.

Among other things, they say Prop. 22 precludes gig workers’ inclusion in the workers’ comp system and keeps them from collective bargaining.

The new lawsuit, which they filed in Alameda County Superior Court, states “Because the Legislature has ‘plenary power, unlimited by any provision of this Constitution’ to address workers’ compensation, including occupational safety,an initiative statute cannot limit the Legislature’s authority in this area.”

The lawsuit also says Prop. 22 is too broad because ballot measures are supposed to focus on only one issue: “[It] also attempts to impose other restrictions that are not substantively addressed in the measure.”

The plaintiffs include the SEIU California and the national SEIU, individual drivers and a ride-hailing customer.

“I’m joining together with my fellow ride-share drivers to continue our fight against Prop. 22 because we know that in a democracy, corporations shouldn’t get the final say in determining our laws,” said Saori Okawa, one of the plaintiffs, in a statement.

In a news release, the plaintiffs mentioned other constitutional challenges to state ballot measures and acknowledged that those efforts took a long time.

“In the case of Prop. 187 – which denied undocumented immigrants access to basic education and healthcare – it took nearly five years, multiple appeals, the end of Gov. Pete Wilson’s administration and the passage of federal legislation for the initiative to be struck down,” the plaintiffs said. “It took almost seven years for Prop. 8 – which denied marriage equality to same-sex couples – to make its way to the United States Supreme Court, where it was struck down in 2015.”