American Airlines Group Inc.’s decision to resume booking its flights to capacity drew fire from some of the top U.S. health officials fighting the Covid-19 pandemic.

“There was substantial disappointment with American Airlines,” Robert Redfield, director of the Centers for Disease Control and Prevention, said at a Senate hearing Tuesday. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said he wasn’t sure “exactly what went into that decision-making” by the carrier.

“I would hope that there would be something to mitigate against that,’ Fauci said, emphasizing the importance of avoiding crowds and wearing face coverings. “In the confines of an airplane, that becomes even more problematic.”

The remarks raise the stakes for American, which along with its rivals is trying to coax customers back onto planes after the coronavirus gutted travel demand earlier this year and prompted a government rescue. American is joining United Airlines Holdings Inc. in selling all the seats it can. Delta Air Lines Inc. has said it will keep middle seats open through Sept. 30, while Southwest Airlines Co. has committed to blocking them unless customers are traveling together.

‘Unwavering’ Commitment

American reiterated that it was confident in the safety of its policy change, given a suite of other measures it’s taking to prevent the virus’s spread. Like other major airlines, it’s requiring passengers to wear face masks and stepping up cleaning efforts.

“We are unwavering in our commitment to the safety and well-being of our customers and team members,” said Ross Feinstein, a spokesman for Fort Worth, Texas-based American. “We have multiple layers of protection in place for those who fly with us, including required face coverings, enhanced cleaning procedures, and a pre-flight Covid-19 symptom checklist.”

American said last week that it would abandon caps on passenger loads starting July 1, while allowing customers to change their reservations at no cost if they want to avoid crowded planes.

The carrier’s policy is under CDC review, Redfield said in response to questions at the hearing from Senator Bernie Sanders.

Rising Caseloads

Faced with a collapse in business, U.S. airlines have received $25 billion in payroll assistance from the government and have access to another $25 billion in loans.

Coronavirus cases have climbed in several states in the last week. There are currently about 40,000 new cases a day, a number that Fauci said could rise to 100,000 if the U.S. doesn’t change its approach to fighting the virus.

The U.S. has recorded more than 2.6 million Covid-19 cases in total, with more than 126,000 deaths from the virus, according to data compiled by Johns Hopkins University.