Four Democratic senators want ExxonMobil to turn over any documents showing the company donated to a group that sent money to anti-climate change researchers, according to a letter sent Thursday.

Massachusetts Sens. Elizabeth Warren and Ed Markey, Rhode Island Sen. Sheldon Whitehouse and Connecticut Sen. Richard Blumenthal signed a letter to ExxonMobil CEO Rex Tillerson. The senators want Tillerson and ExxonMobil to turn over any evidence the company, its foundation or its affiliates donated, or matched employee donations, to Donors Trust and Donors Capital Fund.