NEW YORK (CNN/Money) - The U.S. Department of Justice has served subpoenas on several computer memory-chip makers, including industry leaders Samsung Electronics and Micron Technology, as part of a sweeping investigation into alleged anticompetitive practices.

Other memory-chip makers have acknowledged they too are under scrutiny, but so far no specific demands for information have been made.

Shares of Micron (MU: down $2.70 to $20.90, Research, Estimates), the world's second-largest supplier of dynamic random access memory, or DRAM, and the only major U.S.-based memory-chip maker, fell sharply on the news, trading 11 percent lower on the New York Stock Exchange early Wednesday afternoon.

News of the Justice Department investigation added pressure to the stock, which also was being dragged down by downbeat profit forecasts from computer industry players Advanced Micro Devices and Apple Computer.

Micron, based in Boise, Idaho, confirmed late Tuesday that it received a grand jury subpoena from the U.S. District Court for the Northern District of California seeking information relating to the investigation.

The company said it informed Justice's antitrust division that it will cooperate fully with the investigation, but would not specify the information it has been ordered to surrender.

"Micron does not believe it has violated U.S. antitrust laws," said Kipp Bedard, Micron's vice president of corporate affairs. "The DRAM business is highly competitive and subject to extreme volatility. Competitive forces in today's market have led to DRAM prices reaching unprecedented lows."

American depositary shares of German memory-chip maker Infineon Technology (IFX: down $0.44 to $15.34, Research, Estimates) also were pressured, trading down nearly 3 percent.

Infineon, the world's No. 4 DRAM supplier, said it had been approached by the Justice Department, but no specific demands had been made.

"Infineon will, of course, cooperate with officials conducting the investigation," a spokesman said. "At this time it is not known if Infineon is being investigated or is just required to provide information."

Meanwhile, South Korea's Samsung, the world's largest DRAM producer, said it had received a subpoena from the Justice Department but declined to say specifically what information the agency demanded.

"We can confirm our U.S. subsidiary has received a U.S. court notice saying it will start investigation into a possible violation of the U.S. antitrust law," a Samsung spokesman in Seoul told Reuters.

It was unclear if South Korea's Hynix Semiconductor, the No. 3 DRAM supplier, had been subpoenaed. Toshiba, which sold a U.S. DRAM production facility to Micron in December, said it had not been approached.  

--from staff and wire reports