On Wednesday it was reported that President Trump intends to withdraw from the Paris accord on climate change, two senior White House officials told CNN. The decision, which has yet to be formally confirmed, would break the U.S. from its global partners in the fight to curb global warming.

Should the president pull out, it would mean the U.S. would be one of only three nations in the UN climate group to not sign the deal. (Currently, only Syria and Nicaragua have not signed.) In seceding, the U.S. would become the largest producer of greenhouse gas emissions not included in the agreement.

In response, numerous big cities have vowed to break with Washington in hopes of reinstating the country’s commitment to the environment. Multiple city leaders publicly stated their decision to abide by the accord, whether or not President Trump is on board.

New York City Mayor Bill de Blasio promised to uphold the agreement, going so far as to attack President Trump for ignoring his city’s needs.

“President Trump should know that climate change is a dagger aimed straight at the heart of New York City,” the mayor tweeted on Wednesday. “We’ll take matters into our own hands.”

Likewise, Chicago Mayor Rahm Emanuel issued a strong condemnation of what he called an “alarming” decision to ignore the consensus of 194 countries and the entire scientific community.