Prior to his role at the EPA, he was a partner and the head of the administrative law group at Hunton & Williams, where he lobbied on behalf on major industrial companies and advocated for looser environmental regulations.

[9] According to The New York Times, "Wehrum worked for the better part of a decade to weaken air pollution rules by fighting the Environmental Protection Agency in court on behalf of chemical manufacturers, refineries, oil drillers and coal-burning power plants.

[4] While serving in the Trump administration, Wehrum pushed for rollback of environmental regulations at the EPA, while, according to the New York Times, he "at times continued to interact with former clients, despite an ethics rule that prohibits former industry lawyers and lobbyists from meeting with former clients in private settings to discuss government-related matters for two years.

"[4] The House Energy and Commerce Committee launched an investigation on April 11, 2019, into whether Wehrum had improperly aided his former industry clients since joining the administration.

[11] In addition to his work to change how the EPA calculates the number of deaths attributed to fine particulate matter,[12] Wehrum has been reported to be instrumental in a proposal released in 2018 to "dramatically weaken a major environmental regulation covering mercury, a toxic chemical emitted from coal-burning power plants.