Wyoming and Montana are asking the U.S. Supreme Court to rule on Washington State’s denial of a permit for a port facility that could boost U.S. coal exports.

Both states argue in a filing Tuesday the denial violates the U.S. Constitution. Washington State in 2017 denied a key permit for the Utah-based Lighthouse Resources to be able to proceed with its $680 million coal terminal project in Longview, Washington.

Wyoming Gov. Mark Gordon said Tuesday the denial is a “de facto blockade” on coal-mining states. A spokesman for Washington Gov. Jay Inslee says Washington will continue to defend its decision.