The Trump administration on Wednesday sued the state of California for participating in a cap-and-trade program with Quebec to reduce carbon pollution. According to a press release from the Justice Department, the lawsuit argues that it is unconstitutional for California, as a state, to partner with the Canadian province without the federal government’s approval. “The state of California has veered outside of its proper constitutional lane to enter into an international emissions agreement,” said Assistant Attorney General Jeffrey Bossert Clark of the Justice Department’s Environment and Natural Resources Division in the release. “The power to enter into such agreements is reserved to the federal government, which must be able to speak with one voice in the area of U.S. foreign policy.”

California’s cap-and-trade program puts a limit on planet-warming greenhouse gas emissions, but lets corporations trade emissions “credits” within that cap. “California’s unlawful cap-and-trade agreement with Quebec undermines the President’s ability to negotiate competitive agreements with other nations, as the President sees fit,” Clark said. Wednesday’s lawsuit follows several other efforts from the Trump administration to curtail the state’s work to address climate change. Earlier this year, the president threatened to withhold federal highway funding from California over purported inaction on air quality. The administration has also accused the state of failing to meet federal water quality standards—a claim that was contested by EPA experts.