Sen. Elizabeth Warren (D-MA) speaks with the media following the Democratic policy luncheon on Capitol Hill in Washington, D.C., U.S., March 14, 2017. REUTERS/Aaron P. Bernstein

(Reuters) - Shares of TransDigm Group Inc TDG.N fell as much as 7.3 percent to $250.18 on Monday, after Massachusetts Senator Elizabeth Warren called for an investigation into the aircraft components supplier's government contracts.

TransDigm may have avoided sharing cost information with the government for parts for which it is the sole source supplier, Warren wrote in a letter dated May 19 to Acting Inspector General Glenn Fine at the U.S. Department of Defense.

The company could have also "unreasonably raised prices" on many parts shortly after completing acquisitions of the companies that produce them, Warren's letter suggested. (bit.ly/2sUQxO5)

Cleveland, Ohio-based TransDigm gets about 30 percent of its sales from the defense industry.

The company is already facing heat from U.S. Congressman Ro Khanna, who in March asked the Department of Defense for a probe into its business practices “for potential waste, fraud and abuse in the defense industrial base”.

TransDigm has also been targeted by short-seller Citron Research, which issued a critical report in January suggesting that the company was vulnerable to pricing pressure as President Trump pressured defense contractors Boeing Co BA.N and Lockheed Martin Corp LMT.N, two of TransDigm's major customers, to reduce costs.

However, some analysts refuted Citron’s arguments and attributed TransDigm’s strong margins mainly to its substantial exposure to the aerospace aftermarket and meaningful contributions from acquisitions.

Up to Friday's close, TransDigm's stock had risen 8.4 percent this year, compared with a 13.3 percent increase in the Dow Jones U.S. Aerospace and Defense index .DJUSAE.