Coal mining company Lighthouse Resources sued Washington state in federal court Wednesday for denying a permit to build an export terminal to ship western coal to Asia.

Lighthouse, filing suit in U.S. District Court in Tacoma, argues Washington Gov. Jay Inslee, a Democrat, and the state’s Department of Ecology violated the Constitution’s commerce clause in denying the permit for what would be America’s largest coal export terminal.

“It’s no secret that Washington state officials are philosophically opposed to coal,” said Everett King, president and CEO of Lighthouse. “But that does not give them legal authority to discriminate against this project and block foreign trade and interstate commerce.”

Lighthouse had proposed building the Millennium Bulk Terminal on the Columbia River to ship coal from Wyoming and Montana to Japan, South Korea, and China. The company says an existing Washington state lease already allows coal exports at the site, which Lighthouse seeks to redevelop.

Washington’s Department of Ecology in September denied the terminal a water quality certification, saying it would harm the environment. That halted the project.

Lighthouse estimates the terminal would ship 44 million tons of coal a year, and increase the annual value of U.S. exports by more than $2.5 billion.