The Department of Justice is understood to have issued subpoenas to NVIDIA (NVDA. O) and other companies seeking evidence that NVIDIA violated the Antimonopoly Act, reflecting the escalation of the investigation. The Justice Department, which previously only sent out questionnaires to the companies involved, has now issued a legally binding request for information from recipients, according to people familiar with the matter. That means the government's investigation is one step closer to formally filing a lawsuit. Antitrust officials are concerned that NVIDIA is making it harder for customers to switch to other suppliers and punishing buyers who do not use its artificial intelligence chips exclusively, the people said. Representatives for both the Justice Department and NVIDIA declined to comment.