Numerous airlines, including two major US carriers, operate the Boeing 737 Max 9
Following the Alaska Airlines incident, the Federal Aviation Administration grounded US-based planes with similar mid-cabin door plugs pending inspections. At least 11 companies in the world use the aircraft, though some don't operate in the US.
Table showing the numerous world airlines operate with the the Boeing 737 Max 9 aircraft. United Airlines have the most: 78.