The United States on Wednesday sued California and other state entities for entering a climate agreement with a Canadian province, saying the state had no right to conduct foreign policy, in the latest feud between the Trump administration and the state.

“The state of California has veered outside of its proper constitutional lane to enter into an international emissions agreement. 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,” said Assistant Attorney General Jeffrey Bossert Clark said in a statement.

The U.S. Justice Department said California, state officials, the California Air Resources Board, and the Western Climate Initiative Inc entered a complex cap-and-trade emissions-curbing climate program with Quebec in 2013 without congressional approval.

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Environmental lawyers said on Wednesday that California‘s Republican and Democratic governors, who designed the cap-and-trade system and authorized its linkage with Quebec’s market, were on “solid legal and constitutional ground.”

In cap and trade markets, governments set a steadily declining limit on emissions, and polluters that cut emissions quickly can sell credits to others that need more time. The pact that links California and Quebec’s emissions-trading programs is called the Western Climate Initiative.

In the lawsuit, the latest confrontation with California over the state’s aggressive approach towards combating air pollution and climate change, President Donald Trump’s administration argues that the constitution prohibits states from making treaties or pacts with foreign powers.

‘Head in sand’

“The White House is yet again continuing its political vendetta against California, our climate policies and the health of our communities,” California Governor Gavin Newsom said in a statement. “This latest attack shows that the White House has its head in the sand when it comes to climate change and serves Derekno purpose other than continued political retribution.”

California, the most populous state and one of the top 10 largest economies in the world, has positioned itself as a leader on climate change action in the absence of federal leadership on the issue.

Trump, a Republican who questions the science behind climate change, has eased regulations on the oil, gas and coal industries and intends to pull the United States out of the 2015 Paris agreement on climate change.

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“California and Quebec are modeling an innovative, legally and environmentally robust program that cuts pollution and delivers economic incentives for cleaner energy, fuels and business practices,” said Derek Walker, vice president of the Environmental Defense Fund advocacy group.

The Trump administration in September said it would revoke California‘s authority to set strict car pollution rules that nearly two dozen states had adopted. Those states, including New York, New Mexico and Minnesota, sued the administration to prevent Trump from blocking the California standard

Last month, the Trump administration sent a letter to Newsom, a Democrat, accusing the state of violating clean water laws by allowing human waste from homeless residents to enter its waterways.

Hundreds of former EPA employees are urging a congressional probe into whether the agency’s feud with California represents retaliation for the state’s failure to support Trump’s political agenda.

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This marks the latest in a string of lawsuits that the Justice Department has filed against California throughout the Trump administration.

The department previously sued the state over so-called “sanctuary” laws that limit how state and local authorities cooperate with immigration officials

The Justice Department has also sued over a state “net neutrality” law that aims to create an equal playing field to prevent major internet providers from blocking, slowing down or giving preferential access to online content.