The head of the Senate Armed Services Committee called possible Pentagon plans to retroactively demote retired Army Gen. David Petraeus "disgraceful" and promised a full congressional investigation into the issue.

"I think we need to find out why all of this happened and whether there was any reason behind a four-year delay," said Sen. John McCain, R-Ariz. "I've never seen anything like it."

On Tuesday, defense officials confirmed that Defense Secretary Ash Carter is reviewing whether Petraeus — who pleaded guilty last year to a misdemeanor charge of mishandling classified information — should retain the status and pension of a retired four-star officer.

Petraeus was fined $100,000 and sentenced to two years of probation for the crime of sharing classified information with his personal biographer, with whom he was also having an extramarital affair.

Those revelations also forced him to resign as director of the Central Intelligence Agency in 2012.

McCain and other members of the Senate Armed Services Committee said they had no knowledge of the potential demotion until news reports surfaced this week. Committee ranking member Jack Reed, D-R.I., said his only information so far has been "what I've read in the papers."

McCain said he intends to send a letter to defense officials requesting more information and justification for such a move.

Along with the public disgrace of a demotion, the move could shave more than $40,000 off Petraeus' estimated $220,000 annual military pension.

Before he retired in November, former Army Secretary John McHugh recommended that Petraeus' final paygrade remain unchanged. That suggestion is getting closer scrutiny from Carter's staff, with reports that Petraeus could become a high-profile example of the importance of safeguarding sensitive information.

Petraeus served as the top war commander in Iraq and Afghanistan, and still elicits respect among defense advocates and lawmakers on Capitol Hill. His name had been floated by supporters as a future candidate for national office before his affair was uncovered.

Reporter Andrew Tilghman contributed to this story. 

Leo Shane III covers Congress, Veterans Affairs and the White House for the Military Times newspapers. He can be reached at lshane@militarytimes.com.