Organized labor is laying the groundwork for an aggressive legal challenge to right-to-work laws, one that essentially would invalidate most state versions of the law. The challenge could find its way to the Supreme Court next year, conservative groups say.

The challenge — which unions have advanced in Idaho, Indiana, Wisconsin and just this month in West Virginia — argues that state right-to-work laws, which prohibit workers from being forced to join or otherwise financially support a union as a condition of employment, amount to an unfair “taking” of union funds.