The Department of Justice is suing California over the state's cap-and-trade agreement with Quebec.
The civil lawsuit announced Wednesday is another front in the Trump administration's fight with California.
The Environmental Protection Agency and Department of Transportation said in September they were withdrawing the state's waiver to set fuel economy standards. California countered by suing the DOT with 22 other states.
"The state of California has veered outside of its proper constitutional lane to enter into an international emissions agreement," Assistant Attorney General Jeffrey Bossert Clark of the Justice Department's Environment and Natural Resources Division said in a statement. "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 unlawful cap-and-trade agreement with Quebec undermines the President’s ability to negotiate competitive agreements with other nations, as the President sees fit," Bossert said.
California struck the agreement with Quebec in 2013.