The U.S. Federal Aviation Administration (FAA) said on Monday it has ordered inspections of 2,600 Boeing 737 airplanes because passenger oxygen masks could fail during an emergency.

The FAA said it required the inspections of 737 MAX and NG airplanes after multiple reports of passenger service unit oxygen generators shifting out of position. The issue could result in failing to provide supplemental oxygen during depressurization.

Boeing issued a bulletin to airlines calling for visual inspections on June 17, the FAA added.

The FAA said its airworthiness directive was immediately effective and requires inspections and corrective actions if needed within 120 to 150 days based on the 737 model.

Airlines must conduct a general visual inspection and, if needed, replace oxygen generators with new or serviceable oxygen generators, strap thermal pads, and reposition impacted oxygen generators, the agency said.