Toyota Motor Corp on Tuesday said a U.S. grand jury has ordered it to turn over documents related to problems with rods that connect vehicles' steering systems to their front wheels.

The grand jury subpoena deepens the legal problems facing Toyota, which was once considered a benchmark for high vehicle quality, but has recalled more than 8 million vehicles worldwide since late 2009.

These recalls mainly concern unintended acceleration, including pedals that stick or get caught under floor mats.

Toyota said it was complying with the subpoena -- which was at least the third one to be received by the automaker this year. A Toyota spokeswoman said a U.S. unit received the latest subpoena from a federal grand jury in Manhattan on June 29.

It is unclear which models and model years are covered by the latest subpoena. In May, the National Highway Traffic Safety Administration opened a probe into the timing of a September 2005 Toyota recall for a steering relay rod problem.

The office of U.S. Attorney Preet Bharara in Manhattan did not immediately return a call seeking a comment.

Toyota in February got a subpoena from a federal grand jury in Manhattan related to unintended acceleration, and the next month got one from Michigan Attorney General Mike Cox seeking information on recalls regarding the problem.

A grand jury probe raises the possibility of criminal charges, on top of dozens of civil lawsuits that could cost Toyota billions of dollars in damages.

The NHTSA probe questions whether Toyota notified the agency of a steering rod defect within five business days, as required by U.S. law.

Toyota in 2004 conducted a recall in Japan of Hilux trucks with defective steering relay rods, but at the time told U.S. regulators the defect was isolated to vehicles in Japan, the NHTSA said.

The automaker later admitted the problem affected vehicles sold in the United States. Its 2005 U.S. recall covered about 978,000 vehicles, including the 4Runner sport utility vehicle and pickup trucks from the 1989-1996 model years.

The U.S. government ordered Toyota in April to pay a $16.4 million fine for delaying a January recall over accelerator pedals that did not spring back as designed.

Toyota shares closed Tuesday down 2.6 percent. The benchmark Nikkei average was down 1.2 percent.

(Reporting by Sachi Izumi in Tokyo and Jonathan Stempel in New York; Editing by Maureen Bavdek)