Acting Secretary of Defense Patrick Shanahan is under investigation by the Pentagon’s internal watchdog for allegedly boosting his former company, Boeing, while on the job.

In a Wednesday statement, the Department of Defense inspector general said it “decided to investigate complaints we recently received,” which might show that Shanahan acted “in violation of ethics rules.”

This is a big deal, and it threatens to put the permanent role of Pentagon chief out of Shanahan’s reach for good.

On March 13, the Citizens for Responsibility and Ethics in Washington — a nonprofit organization focused on government accountability — filed an ethics complaint with the Pentagon’s inspector general. Citing news reports, the complaint alleges that Shanahan, in his capacity as deputy secretary of defense, repeatedly championed Boeing’s aircraft over Lockheed Martin’s in official conversations.

Before joining the Pentagon as former Defense Secretary Jim Mattis’s No. 2 in 2017, Shanahan spent decades at Boeing and became one of its top executives. He officially recused himself from any decisions related to Boeing to avoid a situation just like this one from possibly arising.

Then on March 14, Sen. Richard Blumenthal (D-CT) asked Shanahan directly if he would welcome such a probe, to which Shanahan responded, “Yes, I do.”

That may have played a factor in getting the Pentagon’s watchdog to look into the issue. It remains to be seen whether Shanahan will still be as supportive of the investigation as it progresses.

In a statement, Shanahan spokesperson Army Col. Joseph Buccino said the defense chief is fine with the development.

“Shanahan has at all times remained committed to upholding his ethics agreement filed with the DOD,” said Buccino. “This agreement ensures any matters pertaining to Boeing are handled by appropriate officials within the Pentagon to eliminate any perceived or actual conflict of interest issue with Boeing.”

What the ethics complaint alleges Shanahan did

Politico reported in January that Shanahan was under scrutiny for favoring Boeing while at the Pentagon, an issue that has worried lawmakers since his confirmation hearing.

Citing unnamed US officials, Politico said that Shanahan had dissed Lockheed Martin’s production of the F-35 fighter jet in “high-level Pentagon meetings” — at one point calling the plane “fucked up” and saying that the company “doesn’t know how to run a program.” If the fighter jet contract had gone “had gone to Boeing,” he reportedly said, “it would be done much better.”

There’s a fierce rivalry between Boeing and Lockheed Martin that has lasted for decades. It’s no surprise that someone like Shanahan — who spent 30 years at Boeing — would absorb some anti-Lockheed sentiment during his time there.

But he’s supposed to keep those feelings to himself while he serves as a top US official, and even more so as the Pentagon’s (acting) chief. It seems he may not have done that — and could potentially pay the price for it.