“Our space is aviation safety and their space is public health,” FAA Administrator Stephen Dickson told the Senate Commerce Committee on Wednesday, referring to the Centers for Disease Control and Prevention (CDC).

Dickson also cited Transportation Secretary Elaine Chao’s policy that new guidelines encouraging the use of face coverings “will not be regulatory mandates.”

The FAA’s deferment was met with concern by at least two senators, including Sen. Brian Schatz, a Democrat from Hawaii, who expressed frustration over the agency’s neutral approach to the issue.

“Is this, like, a philosophical thing with you folks?” he asked. “I just don’t get why you wouldn’t want this to be mandatory.”

Most U.S. airlines currently require passengers to wear face-coverings throughout their travels and many have recently begun cracking down on travelers who attempt to skirt the rules. On Wednesday, American Airlines removed a man from a flight from New York to Dallas after he refused to wear a mask in the cabin.