Senator Tommy Tuberville, a Republican from Alabama, said last month he would seek to hold up Defense Department nominees who require Senate approval due to the Pentagon's decision to assist troops who have to travel to receive reproductive health care.

"The effects are absolutely critical in terms of... the impact on the force," Austin told the Senate Armed Services Committee of the delays.

"Not approving the recommendation for promotions actually creates a ripple effect through the force that makes us far less ready than we need to be."

Between the Ukraine conflict, an aggressive China and Iran-backed forces attacking US troops in Syria, this is "one of the most complex times that we've seen lately," Austin said.

He noted that upcoming vacancies requiring Senate approval include the chiefs of the US Army, Marine Corps and Navy, as well as the chairman of the joint chiefs of staff.

Senate Majority Leader Chuck Schumer, a Democrat, said Tuesday that "160 routine military promotions" are currently stalled, describing the move as "reckless."

Tuberville -- a Senate Armed Services Committee member -- tweeted in mid-February that because Austin is "following through with his radical plan to facilitate thousands of abortions a year with taxpayer dollars," he would "hold all DoD civilian & general/flag officer nominees that come before the U.S. Senate."

He subsequently described the Pentagon's abortion policy as "illegal," and on Tuesday said during the hearing that his hold on the nominations is "about not forcing the taxpayers of this country to fund abortion."

Austin pushed back, saying the policy is based on "strong legal ground" and calling on Tuberville to reconsider.

"Almost 80,000 of our women are stationed in places... where they don't have access to non-covered reproductive health care," the defense chief said.

The US Supreme Court in June 2022 struck down the decades-old constitutional right to abortion across the country, meaning troops stationed in places that have banned the procedure now have to take leave and travel to areas where it is legal in order to receive care.

In response, Austin told the Defense Department to develop policies -- which were released last month -- to allow servicemembers to take administrative absences in order to receive "non-covered reproductive health care," and to establish travel and transportation allowances to help servicemembers cover costs.