Army combat veteran Sen. Tom Cotton on Tuesday explained his “reservations” with President-elect Joe Biden’s expected choice to serve as secretary of defense in his administration.

Multiple sources with knowledge of the matter told Fox News on Monday night that Biden will nominate retired four-star general Lloyd Austin for the role.

Speaking on “Fox & Friends” on Tuesday, Cotton, R-Ark., said he commends and respects Austin “for his four decades of service to our nation,” but stressed that he has “real reservations.”

“I, like many other senators, have real reservations about giving another waiver under federal law for a recently retired general to become secretary of defense,” Cotton said.

Austin needs a waiver because federal law requires that any general must be “out of the military for seven years” before they can be confirmed as secretary of defense. Austin retired from the military in May 2016.

Cotton, a lawyer, noted that in 2017 a waiver was granted to Jim Mattis, who served as President Trump's first defense secretary.

“I can tell you that senators across the spectrum from liberal Democrats to conservative Republicans are opposed to doing that again,” Cotton said.

Jack Reed is the senior Democrat on the Armed Services Committee. He said at the time in 2017 that he didn't like giving this waiver. It should only happen once in a generation and he wouldn't do it again,” Cotton continued. “A lot of Democrats voted against it as well.”

He went on to say that he suspects “that many senators believe that while General Austin has served our country with distinction and he might be a suitable nomination for many other Cabinet positions, that it’s time to restore proper civil military balance to the Pentagon and granting another waiver might put that at risk.”

Cotton stressed that he will “scrutinize that question very closely” and suspects “most other senators will, too.”

Biden’s long-standing relationship with Austin was a key factor in his selection, a source with knowledge of the matter told Fox News’ Peter Doocy. Austin served as commander of U.S. and coalition forces in Iraq during President Obama’s first term in office.

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If confirmed by the Senate, Austin would be the first Black leader of the Pentagon. Biden is expected to formally announce his pick later this week.

On Tuesday, Cotton also blasted Biden's pick for secretary of Health and Human Services, California Attorney General Xavier Becerra.

As HHS secretary, Becerra would oversee a department that conservatives praised under President Trump for making strides to defend religious liberty and hinder abortion access.

“I woke up this morning with a message from a friend in California who said that Xavier Becerra is so far to the left he makes Bernie Sanders look like a tea partier,” Cotton said.

He then went through “the problems with this nomination.”

“He [Becerra] supports Medicare-for-all,” Cotton said. “He’s going to be responsible for running Medicare and Medicaid and Obamacare and many other health care programs.”

“He’s going to use the discretion the law gives him to try to take away your health insurance on the job, to give less flexibility, less control to families and to states who are in charge of these health care decisions,” he continued.

Cotton said another “problem” is Becerra’s stance on abortion.

“He is a true radical on abortion,” Cotton said. “He supported the lawsuits against nuns. He has gone after pro-life activists in California who expose some truly grisly crimes like Planned Parenthood.”

Cotton then pointed out the current situation in California amid the coronavirus pandemic.

He said that Becerra “has been on the forefront of locking down that entire state, of preventing schools from reopening and people going to church, of defending the kind of decisions we saw over the weekend where the city of Los Angeles will allow a well-connected film crew to set up a canteen in the parking lot of a restaurant, but won't allow that restaurant to serve people right outside their premises.”

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“Xavier Becerra will be Joe Biden’s nationwide lockdown enforcer,” Cotton continued. “The Senate ought not to confirm him.”

Fox News’ Thomas Barrabi and Sam Dorman contributed to this report.