A trio of ride-hail drivers filed a lawsuit in California’s Supreme Court on Tuesday alleging that Proposition 22 is unconstitutional, CNET reported.

The proposition, which allows human cloud, gig economy firms — including Uber Technologies Inc. and Lyft Inc. — to continue classifying their drivers as independent contractors, was approved by California voters in November. Backers of the measure, which included Uber and Lyft, spent more than $200 million to get it passed, Business Insider reported.

Uber and Lyft had been engaged in a court battle with California Attorney General Xavier Becerra, who sued the human cloud firms alleging they were misclassifying their drivers as independent contractors under California’s AB 5 law that gets tough on misclassification.