The US Department of Justice (DOJ) has issued subpoenas to NVIDIA (NVDA.US) and other companies, saying it is seeking evidence that the companies have violated antitrust laws, Bloomberg reported.NVIDIA shares further dived over 2% in after-hours following a 9.5% crash on Tuesday.Related NewsTSMC Sep Rev. Spikes ~40% YoYThe report cited people familiar with the matter as saying that the DOJ had previously sent questionnaires to the companies, and is now sending legally binding requests for information, moving one step closer to a formal complaint within the government investigation process.Antitrust officials are concerned that NVIDIA is making it more difficult to switch to other suppliers and penalising buyers who don't use its AI chips, the sources stated.(Real-time Streaming US Stocks Quote; Except All OTC quotes are at least 15 minutes delayed.)Related NewsNvidia, on Strong AI Demand, Has Shrs Grossed Gains of 25% in 1Mth