Pruitt is skeptical of climate change and wrote in National Review in May that the science is "far from settled." He is also one of the state attorneys general who sued the EPA over the Clean Power Plan, which aims to reduce carbon emissions from power plants.

He also has ties to the energy industry. In 2014, the New York Times discovered that a 2011 letter Pruitt sent to the EPA was actually written by lawyers for an energy company in Oklahoma. The letter from Pruitt had "only a few word changes," according to the New York Times.

Senate Democrats plan to pressure Republicans who do believe in climate change to oppose Pruitt's nomination.

"We have enough votes to prevent him from going forward if they'll stick with us," Sen. Sheldon Whitehouse (D-RI) said, according to CNN.

Whitehouse also said that companies who believe the country should address climate change should also speak out against Pruitt's nomination.

"If not, we will end up with an EPA that has been corrupted by the fossil fuels industry," he said, per CNN.