Corrected 5:07 p.m. | Key Senate Armed Services Committee members on Tuesday said they would vote against waiving a law that would prohibit President-elect Joe Biden’s choice for Defense secretary from assuming the role of Pentagon chief amid concerns about civilian control of the military.

Retired Army Gen. Lloyd Austin is Biden’s pick for Defense secretary, but the former U.S. Central Command chief falls three years short of the seven-year “cooling off period” for a former officer to take the Pentagon’s top civilian post. Lawmakers in both chambers would need to vote to waive that law for the Senate to proceed to his confirmation.

Among those who said they will vote “no” on the waiver are Sens. Elizabeth Warren, D-Mass., Tammy Duckworth, D-Ill., and Richard Blumenthal, D-Conn..

Arkansas Republican Sen. Tom Cotton questioned whether Austin’s experience was the best fit for the Defense secretary role, but did not indicate how he would vote on the waiver. Others, including Sens. Tim Kaine, D-Va., and Angus King, I-Maine, said they were undecided.

The waiver may be the highest hurdle to Austin’s confirmation. Duckworth, for one, has said she would support his confirmation if Congress agrees to waive the law.

Retired Gen. James Mattis, who was President Donald Trump’s first Defense secretary, was granted the same waiver at the start of Trump’s term in 2017. Mattis was the second person in history to be granted such a waiver.

Granting another waiver so soon after Mattis’, some lawmakers have argued, calls into question civilian control of the military.

“There are important principles and values at stake here,” Lindsay Cohn, an associate professor at the U.S. Naval War College, said in her opening remarks at a Senate Armed Services Committee hearing.

“On the pro side of granting the waiver are the principles that the president should be able to choose his own people, and the principle of breaking down diversity barriers in the national security world,” Cohn said, referencing that Austin would be the first Black man to lead the massive department.

“But on the con side, there are the issues of civilian control of the military — a bedrock of American democracy — and issues of democratic governance,” Cohn said.

Cohn also highlighted the issue of public trust in the American political system, and said that Austin’s nomination furthers the notion that military officers are more trustworthy than civilian bureaucrats — an idea that Cohn called “hugely problematic” at a time when faith in the political system is at a low point.

Kathleen J. McInnis of the Congressional Research Service, said there is significant, public evidence that civilian voices within the Defense Department have been muted because of a deference to military leaders.

Both experts agreed that when that happens, important policy positions are overshadowed by a militaristic approach to problem-solving.

“Austin must understand that, if confirmed, he is in a political role of bureaucratic politics and must rely on the expertise of others,” Jack Reed of Rhode Island, the committee’s top Democrat, said.

Lawmakers, many of whom participated in the hearing virtually, wondered whether granting Austin a waiver would create a “new norm.”

“I have immense respect and admiration for Austin, but we are now in danger of setting a precedent of a new norm — creating a danger that the exception will swallow the rule,” King said.

Cotton, who was joined by Alaska Republican Dan Sullivan, took issue with the notion of a weakening civilian control at the Pentagon.

“I don’t think anyone believes civilian control of the military is seriously at risk from Austin,” Cotton said, “but the real question is whether the experiences, skills and relationships that retired military officers bring to the job is right for the role of Defense secretary?”

Both Cohn and McInnis said they were not.

“The job of Defense secretary is incredibly difficult. Both Mattis and George Marshall, the only other Defense secretary to be granted a waiver, relied heavily on their military experience and were not shining examples of the best we can do,” Cohn said.

Chairman James M. Inhofe, R-Okla., asked the witnesses what sort of questions they should ask Austin during his nomination hearing, should he be granted a waiver.

“Ask him: How does he plan on demonstrating a commitment to the civilian side of the Pentagon? How does he see the differences between his role a Defense secretary and his role as a general?” Cohn said.

Both experts agreed that if confirmed, Austin should avoid overusing his military background, instead favoring a broader, more political approach to the position of Pentagon chief, including a willingness to engage with the press and with lawmakers.

This report has been revised to reflect that Sen. Angus King, I-Maine, was undecided on the waiver.