In the letter, which was published by Politico Tuesday evening, the Democrats who sit on the Environment and Public Works Committee noted that the ties between Pruitt and an Oklahoma energy company, as well as a group funded by the Koch brothers, have been previously reported in the news.
The New York Times reported in 2014 that a letter from Pruitt's office to the EPA was written by lawyers for Devon Energy, with a few words changed. The senators also noted that Pruitt is a board member at the Rule of Law Defense Fund, which receives funding from the conservative billionaire Koch brothers.
The Democratic senators asked Pruitt to explain his role in the Rule of Law Defense Fund, as well as to provide a list of the group's donors and expenditures. They also asked for any communications and meetings Pruitt had with the fund, in addition to any legislation on issues that the group had taken a position on.
The letter was signed by Sen. Sheldon Whitehouse (D-RI), Sen. Jeff Merkley (D-OR), Sen. Bernie Sanders (I-VT), Sen. Edward Markey (D-MA), Sen. Cory Booker (D-NJ) and Sen. Ben Cardin (D-MD).
Democratic senators have said that they will work to block Pruitt's nomination to lead the EPA and plan to put pressure on Republican senators who have publicly said that they believe in climate change.
Pruitt is a climate change skeptic who wrote in the National Review in May that the science behind global warming is "far from settled." He is also one of several state attorneys general who sued the EPA over the administration's plan to reduce carbon emissions.