Shares in the AI chip designer Nvidia have continued to slide overnight after a report said US authorities were ramping up an investigation into whether the company had breached competition laws. The company's shares fell 2.4% in after-hours trading, exacerbating a near-10% drop in the regular trading session that slashed its value by 279bn ( 212bn) to 2.6tn, marking the largest one-day drop in history for a US company. Overnight, the US Department of Justice sent subpoenas to Nvidia and other tech companies, in a move that will force recipients to provide information under law, Bloomberg reported. Officials are said to be concerned the company has made it harder for clients to switch to other semiconductor suppliers and is penalising buyers that refuse to exclusively use Nvidia's AI chips. Such a move would signal an escalation of the US antitrust investigation, and brings the government a step closer to launching a formal complaint against Nvidia. The sell-off on Tuesday came amid a wider sell-off on markets sparked by weak US manufacturing data that raised broader concerns about the outlook for the country's economy among investors.