Democratic presidential candidate Elizabeth Warren called for the head of the Justice Department’s antitrust division to recuse himself from working on any investigations of Alphabet Inc.’s Google or Apple Inc. because of his past lobbying for both companies.

Warren wrote to Assistant Attorney General Makan Delrahim, who oversees the antitrust division, in a letter dated Tuesday that his past work advocating on behalf of the tech giants would create the appearance of a conflict of interest as the agency oversees antitrust scrutiny of both companies. The Massachusetts senator sent a similar letter calling for Delrahim’s recusal to a Justice Department ethics official.

“As the head of the antitrust division at the DOJ, you should not be supervising investigations into former clients who paid you tens of thousands of dollars to lobby the federal government,” Warren’s letter said. “American consumers and markets deserve the confidence that the DOJ will conduct any antitrust investigation into Google or Apple with integrity, impartiality, and with the best interest of competitive markets and consumers in mind.”

Warren’s letter comes days after the Justice Department and Federal Trade Commission divvied up antitrust oversight of Google, Facebook.com Inc., Amazon.com Inc., and Apple.

Under that agreement, the Justice Department will pursue an antitrust investigation of Google and oversee any scrutiny of Apple while the Federal Trade Commission will be responsible for antitrust oversight of Amazon and Facebook. The House Judiciary Committee has also opened a separate investigation into competition issues in the technology industry.

Past lobbying

Google hired Delrahim in 2007, while he worked at the Brownstein Hyatt Farber Schreck LLP law firm, to lobby federal officials around its acquisition of digital advertising company DoubleClick. Google paid the firm at least $100,000 for the work, which officially ended the next year, according to federal lobbying disclosures. The $3.1 billion purchase of DoubleClick, which was approved by the Federal Trade Commission in 2007, could once again be under the microscope in Washington as the Justice Department looks at Google’s dominance in the digital advertising market.

In 2006, Delrahim, a former deputy assistant attorney general in the antitrust division, also started lobbying on behalf of Apple, though the computer maker reported paying his firm less than $20,000 before ending the agreement the next year, federal records show.

Warren has previously criticised the ethics of Delrahim’s position in the department and in 2017 delayed a vote approving his nomination. She described his candidacy for the job as an indication that Trump’s administration would ‘put the interests of giant corporations ahead of the American people,’ according to a 2017 Facebook post by Warren.