The Washington State Supreme Court will hear oral arguments Tuesday over the constitutionality of a tax to fund light rail projects in King, Pierce, and Snohomish counties.

The class-action lawsuit, filed in 2018, claims Sound Transit is unconstitutionally collecting car-tab taxes for the $54 billion Sound Transit 3 package that voters approved in 2016.

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The issue hinges on a 2015 law that allowed a regional transit authority to collect taxes in compliance with the law “as it existed on January 1, 1996.” However, the state legislature did away with the 1996 valuation schedule in 2000 and replaced it with a new schedule in 2006. Plaintiffs argue that should make the 2015 law obsolete.

A Pierce County Superior Court judge dismissed the lawsuit last year, ruling that the 2015 law was constitutional.

If the Supreme Court sides with the plaintiffs, Sound Transit could be forced to refund hundreds of millions in damages to taxpayers, which would threaten light rail projects.

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