Nvidia has received a subpoena from the U.S. Department of Justice as the regulator seeks evidence that the AI-heavyweight violated antitrust laws, Bloomberg News reported Tuesday, citing people familiar with the investigation.

The antitrust watchdog had previously delivered questionnaires to companies, and is now sending legally binding requests, the report said.

Officials are concerned that the chipmaker is making it harder to switch to other suppliers and penalizes buyers that do not exclusively use its artificial intelligence chips, the report added.