Congressional support for a probe into TransDigm's pricing model is getting louder.
CNBC has obtained a copy of a letter sent by Sen. Elizabeth Warren, D-Mass., last month to the U.S. Department of Defense asking for an investigation into the aerospace component supplier's business.
"As a member of the Senate Committee on Armed Services, I have also been monitoring reports that suggest TransDigm WorldWide has used a variety of tactics to avoid sharing cost information with the government for parts for which it is the sole source supplier," Warren wrote in the letter to the DOD's acting inspector general, Glenn Fine, on May 19.
"These reports further show that TransDigm has unreasonably raised prices on many parts shortly after completing acquisitions of the companies that produce them," she wrote.
Warren's call for a probe into the aerospace component supplier follows similar requests from U.S. Rep. Ro Khanna, D-Calif., and U.S. Rep. Tim Ryan, D-Ohio.
Abusing taxpayer money has been a hot topic in Washington, and it is something Warren referenced in her letter as well.
"I look forward to working with your office, and the Department of Defense to ensure that our service members continue to receive the best made equipment while also ensuring that taxpayers continue to receive fair value," wrote Warren to the DOD.
Comments from Warren on TransDigm come as Secretary of Defense Jim Mattis is set to testify in front of the Senate Armed Services Committee this week.
Meantime, TransDigm competitors have also joined the fight.
Following Khanna's comments in March, First Aviation Services' Senior Vice President Josh Krotec wrote to the Defense Department on May 30 saying, "[W]e appreciate Mr. Khanna's shining a light on the tactics that TransDigm uses to create the appearance of competition, while actually protecting (or strengthening) TransDigm's monopoly positions and pricing power over [the] DoD."
TransDigm's alleged use of anticompetitive practices and unfair price hikes of its components post-acquisition has been the central argument behind why Citron Research's Andrew Left has been calling the company the "Valeant of the Aerospace Industry."
"TransDigm acquires airplane parts companies (over 50 in total), fires employees, and egregiously raises prices. This business model has made them a dominant supplier of airplane parts to the aerospace industry while burdening its balance sheet with sky-high debt load," wrote the hedge-fund manager in a report to clients on Jan. 20.
The controversy surrounding TransDigm has garnered the attention of other hedge-fund investors.
According to Factset, which has compiled data from the latest filings, Tiger Global Management is the third-largest holder of TransDigm with a 7.7 percent stake. Other investors, according to Factset, include "Tiger Cub" Blue Ridge Capital, Voya Investment and Principal Global Investors.
The Financial Times has reported that Sophos Capital is short the stock.
So far, the bulls have been winning the race, with TransDigm shares up 8 percent year to date as of Friday's close. However, after word of Warren's letter was made public, the company's share fell about 4 percent Monday.
CNBC requested a comment from TransDigm, but has not yet heard back.