(CNN) The psychiatrist at the center of a whistleblower retaliation case that stalled the confirmation process of President Donald Trump's nominee to lead the Federal Aviation Administration is facing disciplinary action from the state of Illinois in a separate case, CNN has learned.

Documents obtained by CNN show the psychiatrist who handled the evaluation for Delta, Dr. David Altman, currently faces a complaint from an Illinois regulator for allegedly threatening another Delta pilot two years before that referral.

The Illinois Department of Financial and Professional Regulation is seeking the "revocation or suspension" of Altman's medical license, according to a complaint filed against Altman in May by the department and obtained by CNN through a public records request.

The Illinois regulator says that Delta referred a pilot to Altman for a psychiatric review, and after Altman interviewed him in 2014, he wrote a preliminary report and stated that if the pilot took legal action against or complained about Altman (among other things), then that could affect his diagnosis of the pilot and potentially stop him from flying.

Altman "used threat of the possibility of a diagnosis that would result in permanently baring" that pilot "to discourage" him from reporting Altman to the Illinois Medical Disciplinary Board, the complaint alleges.

Altman has denied the department's allegation that his report contained a threat and that his actions are grounds for the revocation or suspension of his license.

Altman did not respond to CNN's request for comment.

Following Altman's preliminary report containing the alleged 2014 threat, an attorney for a union representing Delta pilots wrote a letter to Delta's labor relations department demanding the "immediate removal" of Altman as a medical examiner for the company.

Gordon Rose, an attorney for the Air Line Pilots Association, wrote in a May 2014 letter that a neutral medical examiner would be "seriously disturbed" by Altman's preliminary report about that pilot, which he said crossed "the line of professionalism and appropriate conduct."

At the time, Dickson served as Delta's senior vice president for flight operations.

Despite that protest, Altman continued to conduct psychiatric evaluations for Delta.

2016 case already under scrutiny

It's unclear if Dickson was aware of the alleged threat that Altman made against the other pilot when he later approved the referral of pilot Karlene Petitt in 2016 .

After Petitt shared a list of safety concerns with Dickson, who was still in the same operations oversight role, and another flight operations manager in January 2016, Dickson approved referring Petitt for a mental evaluation.

Altman diagnosed Petitt with bipolar disorder and the company grounded her for more than a year, but two subsequent examinations found that she does not have that disorder, and she is currently flying for Delta.

Delta paid Altman about $70,000 for his psychiatric work with Petitt, according to invoices, which list more than 200 hours of services.

Petitt has sued Delta and argues the company retaliated against her, which Delta denies. Neither Dickson nor Altman are named as defendants in Petitt's case, though their alleged actions are described in the suit.

A Delta spokesperson, Lisa Hanna, said the company disagrees with the characterization that Altman's 2014 report contained a threat and added that Altman last consulted with Delta when evaluating Petitt, for which he was paid his hourly rate.

Hanna said that when the need arises for a medical assessment, Delta's director of health services selects an appropriate medical specialist.

Petitt's attorney Lee Seham previously told CNN that Dickson allowed what amounted to retaliation against his client.

Although Altman's diagnosis was overturned and Delta reinstated Petitt to fly, Dickson said in a response to questions from Democratic senators in May that given the circumstances, he stands by the company's decision to have Petitt's mental health assessed.

"The referral was made based on a credible report about statements the pilot made to company officials and behavior she exhibited, which raised legitimate questions about her fitness to fly," Dickson said.

He added that his involvement with Petitt was limited and stated, "I have not previously and will never tolerate retaliation of any kind to any employee who raises safety concerns."

The FAA substantiated one of Petitt's allegations related to improper pilot scheduling by Delta, according to documents. Delta said that issue had been corrected by the time the FAA investigated it.

On Wednesday, the Senate Committee on Commerce, Science and Transportation approved Dickson's nomination to be FAA administrator with votes split along party lines -- 14 votes in favor and 12 opposed. The full Senate now must vote on his nomination.

At Wednesday's hearing, Sen. Richard Blumenthal, a Connecticut Democrat, described Petitt's experience as "a classic instance of retaliation" and criticized Altman's assessment of Petitt by citing Altman's comments in court earlier this year.

During a trial for Petitt's case before an administrative judge in March, Altman said Petitt's decision to simultaneously care for three children under the age of three while nursing, help her husband's business and attend night school were signs of mania.