The Trump administration on Wednesday moved to topple California as a leading voice against climate change, charging in a federal lawsuit that the state exceeded its constitutional authority by joining with a Canadian province in a program to cut climate-damaging fossil fuel emissions.

In addition to adding to a long list of lawsuits pitting California and other Democratic-led states against the Trump administration over proposed federal environmental rollbacks, the new lawsuit raises constitutional questions about whether President Donald Trump’s inaction on climate change amounts to an international and domestic policy that states must follow, constitutional experts say.

Wednesday’s lawsuit serves as “Exhibit A in the challenges that states face in addressing climate change on their own,” when “this administration doesn’t want to do anything” on the problem, said Cary Coglianese, professor at the University of Pennsylvania Law School.

The complaint, filed in California federal court, names Democratic Gov. Gavin Newsom and others. It alleges California usurped federal power to conduct foreign policy and make international accords when it signed an ongoing agreement with Quebec to limit emissions through a so-called cap and trade program.

Former Republican Gov. Arnold Schwarzenegger started the program, which lets businesses pay to buy pollution credits, in 2006. Quebec signed on about a decade later.

California “veered outside its proper constitutional lane” by signing an international accord, Assistant U.S. Attorney General Jeffrey Bossert Clark said in a statement.

Newsom said Wednesday that the administration was “continuing its political vendetta against California, our climate policies and the health of our communities.” Mary Nichols, head of the state’s air board, promised to “vigorously defend” the state’s cap and trade program in court.

Trump mocks the science of climate change, calls for reviving the sagging U.S. coal industry and expanding the country’s oil and gas boom. As one of the first acts of his presidency, he declared his intention to pull out of the Paris climate accord.

Dozens of states and hundreds of cities since then have joined in alliances supporting the Paris climate accord, with names such as “We are Still In.”

California and other states have filed dozens of legal challenges to administration rollbacks of environmental regulations and laws. Tensions between Newsom and the administration escalated this year, when Trump tried to compel California to join in his proposal to relax Obama-era mileage standards for passenger vehicles.

The Justice Department in August announced it was opening an anti-trust probe of four automakers that agreed to follow California’s tougher mileage standards. Other administration moves against California since then include threatening the state with loss of highway funding over its air pollution.

While states and environmental groups have won many of their legal challenges to Trump rollbacks, three constitutional law experts said Wednesday that the administration may get federal judges’ attention with its complaints about California’s efforts to remain an international climate leader.

“The gist of the complaint … is that California’s conduct interferes with the idea that the nation speaks with a single voice on climate — in this case, by pulling out of the Paris accord,” said Deborah Sivas, a professor at Stanford Law School.

Unlike some administration legal arguments, “this one has some merits … regardless what you think of global warming,” said Josh Blackman, professor at South Texas College of Law.

The Trump administration cannot formally start the year-long withdrawal process from the Paris agreement until Nov. 4, three years after the international accord went into effect.

The process starts with a letter from the United States to the United Nations Secretary-General, but doesn’t go into effect until a year later, which happens to be the day after the 2020 presidential election