Two Senate Democrats are signaling that they will oppose giving retired Gen. Lloyd Austin a waiver to serve as President-elect Joe Biden's Pentagon chief.

The law mandates a Defense secretary must be retired from active service for at least seven years before assuming the top civilian role unless Congress grants a waiver. Austin retired in 2016.

"I have the deepest respect and administration for General Austin and this nomination, and this nomination is exciting and historic. But I believe that a waiver of the seven year rule would contravene the basic principle that there should be civilian control over a nonpolitical military," Sen. Richard Blumenthal (D-Conn.) told reporters on Tuesday. 

"That principle is essential to our democracy. That's the reason for the statute which I think has to be applied, unfortunately, in this instance," he added.  

Blumenthal declined to say if he believed Biden should nominate someone else, but added, "I will not support the waiver."  

Blumenthal was one of 17 Democratic senators who in 2017 voted against providing a waiver to retired Gen. James Mattis, who was President Trump's first pick to lead the Pentagon. A majority in both chambers of Congress ultimately voted to give Mattis a waiver, and he was confirmed by the Senate for the Defense secretary position. 

Sen. Jon Tester (D-Mont.), another one of the 17 "no" votes in 2017, said on Tuesday that he was also unlikely to support granting Austin a waiver. 

"I didn't for Mattis and I don't think I will for him," Tester said, referring to Austin. 

"I love Mattis, I thought Mattis was a great secretary. And I think this guy is gonna be a great secretary of Defense. I just think that we ought to look at the rules," he added. 

Biden hasn't formally named Austin as his pick to lead the Pentagon but sources confirmed to The Hill on Monday night that he had been selected. Austin would be the United States's first Black Defense secretary. He previously served as the first Black chief of U.S. Central Command from 2013 to 2016. 

But Austin comes with baggage, including that he has not been retired from the military for as long as the law requires a Defense secretary to be.  

Even as Blumenthal and Tester indicated that they would likely vote against granting Austin the waiver, other Democrats who voted against giving the same greenlight to Mattis didn't rule out allowing it for Biden's pick. 

Sen. Chris Murphy (D-Conn.), one of the seventeen "no" votes in 2017, said he has concerns about the "erosion of civilian control" at the Pentagon and wants to hear from the incoming administration.  

"I inherently trust the Biden administration on issues of national security in a way that I did not inherently trust the Trump administration. So I'm certainly — given that I'm a believer in his policy, I'm much more willing to give him deference," he said.