At least two lawmakers are calling on all Boeing 737 Max 8 airplanes to be grounded after two were involved in crashes in recent months.

An Ethiopian Airlines flight crashed Sunday, leaving 157 people dead. It was the second Boeing 737 Max 8 to be involved in a deadly crash shortly after takeoff. About four months ago, a Lion Air jet of the same model crashed in Indonesia, killing 189 people.

More than 20 United Nations workers were among those who died in the Ethiopian Airlines flight, which was headed from Addis Ababa to Nairobi, Kenya.

On Monday, Sens. Dianne Feinstein (D-Calif.) and Richard Blumenthal (D-Conn.) called for all Boeing planes of the 737 Max 8 series to be grounded until the aircrafts’ safety could be ensured.

“I write to ask that all Boeing 737 Max 8 aircraft be grounded until their safe use has been confirmed,” Feinstein wrote in a letter to the Federal Aviation Administration. The California lawmaker noted the “troubling similarities” between the recent crash near Addis Ababa and the one near Jakarta last October.

Blumenthal added that the planes of that model should be grounded “until the FAA can assure American travelers that these planes are safe.” He said the crashes less than five months apart were an “alarming tragedy” that called into “serious question” the planes’ safety.

The FAA released a “continued airworthiness notification” late Monday, saying that, although reports were “drawing similarities” between the two crashes, the investigation into the Ethiopian Airlines crash had “just begun and to date we have not been provided data to draw any conclusions.” The U.S. aviation authority added that it had sent personnel to support the investigation into the crash and would take “appropriate action” if needed.

Transportation Secretary Elaine Chao said earlier Monday that she met with the FAA acting chief to discuss the fatal crashes and that U.S. regulators were “very carefully” reviewing them.