Alabama Senator Tommy Tuberville is blocking the quick promotion of the top military aide to Defense Secretary Lloyd Austin over concerns that he and other senior staff did not immediately notify President Joe Biden when Austin was hospitalized with complications from cancer treatment earlier this year.

Biden in July nominated Lieutenant General Ronald Clark to become commander of U.S. Army forces in the Pacific. But Clark has faced criticism from Republicans over his role as one of Austin's top aides when the defense secretary was in the hospital in January and did not tell Biden or other U.S. leaders.

Republicans said the fact that Biden was kept in the dark about Austin not being in command for days could have meant confusion or delays in military action, even though decision-making authorities had been transferred to the deputy defense secretary.

Tuberville's hold comes a year after he came under intense criticism from colleagues in both parties for holding up hundreds of military promotions over a Pentagon abortion policy. The Senate finally approved 425 military promotions and nominations in November after Tuberville relented.

Republican colleagues said they agreed with Tuberville on the abortion policy but openly pressured him to drop the holds, voicing concern about military readiness and the toll it was taking on service members and their families who had nothing to do with the regulations.

A spokeswoman for Tuberville, Hannah Eddins, said Tuesday that the senator has concerns about Clark's role during Austin's hospitalization, including that he did not inform Biden. She said that Tuberville is waiting on an a report from the Pentagon's inspector general that will review the matter.

"As a senior commissioned officer, Lieutenant General Clark's oath requires him to notify POTUS when the chain of command is compromised," Eddins said, using an acronym for the president of the United States.

Majority Democrats could still bring Clark's nomination up for a vote, but Tuberville's hold likely delays his confirmation because several days of floor time would be needed to confirm him. The nomination will expire with the end of the congressional session and the next president would have to renominate Clark or someone else to the post if he is not confirmed by early January.

Pentagon spokesperson James Adams said that Tuberville's new hold, which was first reported by The Washington Post, "undermines our military readiness."

"Lt. Gen. Clark is highly qualified and was nominated for this critical position because of his experience and strategic expertise," Adams said in a statement. "We urge the Senate to confirm all of our qualified nominees."

Austin has come under bipartisan criticism for initially keeping Biden in the dark about his health issues and hospitalization. Austin was admitted to intensive care for complications from prostate cancer surgery on January 1, but the White House was not told until January 4. Austin's senior staff were notified on January 2.

The defense secretary later said he takes full responsibility and had apologized to Biden. Still, Austin insisted that there were no gaps in control of the department or the nation's security because "at all times, either I or the deputy secretary was in a position to conduct the duties of my office."

An earlier Pentagon review of the matter blamed privacy restrictions and staff hesitancy for the secrecy, and called for improved procedures, which have been made.

The White House also laid out a new set of guidelines to ensure it will be informed any time a Cabinet head cannot carry out their job. The new guidelines include a half-dozen instructions for Cabinet agencies to follow when there is a "delegation of authority," or when secretaries temporarily transfer their authority to a deputy when unreachable due to medical issues, travel or other reasons.