The declaration is the outdoor apparel company’s opening salvo in a PR and legal battle against President Trump’s shrinking of two Utah national monuments. Patagonia said the move was “illegal” and constituted the “largest elimination of protected land in American history.”

On Monday, President Donald Trump announced the rollback of Obama and Clinton-era federal land protections that will reduce the size of Bears Ears National Monument in Utah by 85% and halve the size of Utah’s Grand Staircase-Escalante.

Speaking in Salt Lake City Monday, Trumps said the move reverses “federal overreach” and will return control of land to local authorities and citizens. But Native American and environmental protection groups fear removing federal protections paves the way for environmentally destructive corporate activities on land of archaeological significance.

The company Patagonia—which already campaigns to protect swathes of the eponymous wilds in Argentina and Chile—said it would file a lawsuit against the Trump Administration in partnership with local community and environmental groups.

“Americans have overwhelmingly spoken out against the Trump Administration’s unprecedented attempt to shut down our national monuments,” Patagonia President and CEO Rose Marcario said in a statement, according to AdAge. “We’ve fought to protect these places since we were founded and now we’ll continue that fight in the courts.”

Several environmental groups filed a lawsuit hours after Trump’s speech Monday. Earthjustice, which filed on behalf of ten groups including the Wilderness Society and the Natural Resources Defense Council, challenges the reduction of the Grand Staircase-Escalante Monument, according to AP. A coalition of Native American tribes also said it would sue the Trump Administration over the reduction of the Bears Ears Monument.