Several more pilots have come forward to say they too are concerned about the oxygen problems plaguing America's most expensive fighter jet, the F-22 Raptor, according to lawmakers.

On the same day that the Pentagon announced the Air Force had been directed by Defense Secretary Leon Panetta to add new safety measures to F-22 missions, U.S. Sen. Mark Warner (D.-Va.) and Rep. Adam Kinzinger (R.-Ill.) told reporters that a total of nine people involved in the F-22 program, a majority of them pilots, have now contacted them directly about the troubled plane. Kinzinger was on hand when two F-22 pilots, Josh Wilson and Jeremy Gordon, spoke out about their fears flying the F-22 in a CBS News' "60 Minutes" interview earlier this month.

As a recent ABC News investigation found, for more than four years pilots in the F-22 Raptor, which cost more than an estimated $420 million each, have reported at least 25 instances of experiencing "hypoxia-like symptoms" in mid-air. In one instance, a pilot became so disoriented by an apparent lack of oxygen that his plane dipped down and skimmed treetops before he managed to save himself, an Air Force spokesperson told ABC News.

Despite investigating the source of the problem for years - and even grounding the full fleet for nearly five months last year - the Air Force still does not know what is wrong with the planes. The service also does not know what caused the malfunction that contributed to the death of F-22 pilot Capt. Jeff Haney in November 2010.

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The Air Force has said that any pilots that request not to fly the plane will not be punished and the Virginia Air National Guard, for whom Wilson and Gordon fly, told ABC News the command would "not consider using disciplinary action as a means of reprisal" against them. However, the Congressmen and an attorney for the pilots said that Wilson still has a letter of reprimand from the Guard and could face a flying evaluation board.

"If a pilot feels uncomfortable flying this aircraft, they shouldn't be forced to," said Kinzinger, a veteran fighter pilot himself. Both Kinzinger and Warner said they wanted to create a space where concerned pilots and others in the program could come forward without fear of professional reprisal.

READ: Panetta Demands F-22 Raptor Fighter Fixes After Mid-Air Scares