If President-elect Donald Trump wants to pull the U.S. out of the Paris climate deal, he’ll face an unlikely foe: corporate America. More than 300 companies and major investors signed a letter urging Trump to roll back his campaign promises and leave low-emissions policies in place.

In the joint letter sent from Marrakesh, Morocco, where the fine points of implementing the Paris Climate Agreement are being hammered out, major American companies like Gap, General Mills, Intel, and Monsanto wrote to “re-affirm our deep commitment to addressing climate change through the implementation of the historic Paris Climate Agreement.”

The letter, signed by 68 companies with more than $100 million in annual revenue, was addressed directly to Trump, President Obama, and members of the U.S. Congress. The Paris Agreement is a global initiative to limit global warming, prepare for climate change, and promote clean energy.

Canceling the Paris deal and other global climate accords was a key campaign promise by Trump. He has said in the past that climate change is a hoax invented by the Chinese “in order to make U.S. manufacturing non-competitive.” His appointee to oversee transition of the Environmental Protection Agency is a leading climate change skeptic, and he’s promised to roll back Obama Administration regulations on oil, gas, and coal, as well as open up more federal lands for energy extraction.

But corporate America, which has been preparing for the business disruption that will be caused by climate change, could become a significant hurdle for Trump. Signers of the letter include some of the world’s biggest food conglomerates including Mondelez International, Kellogg Company, and Mars Inc. Notably absent are representatives of the oil, gas, coal and automotive industries.

“Climate change, water scarcity, and deforestation are serious threats to society,” Mars chief sustainability officer Barry Parkin said in the statement. “It is imperative that global businesses, like Mars, do their part to face down those threats.”