It also said it will tighten oversight of Boeing itself, after a cabin panel broke off a new jet mid-flight.
Alaska Airlines and United Airlines, the two U.S. carriers that use the aircraft involved, have had to cancel hundreds of flights.
They've both grounded all MAX 9 flights through Tuesday, and United canceled some additional flights in the following days.
The Federal Aviation Administration says it will require another round of inspections before considering putting the jets back in service.
Under more stringent supervision, the regulator will audit the Boeing 737 MAX 9 production line and suppliers.
It'll also consider having an independent body take over aspects of certifying the safety of new aircraft from Boeing that the FAA previously assigned to the planemaker.
The FAA said the continued grounding of 171 planes with the same configuration as the one in the incident was "for the safety of American travelers."
Boeing is facing a widening crisis. Its shares closed down 2.2% on Friday and down nearly 12% since the January 5 incident.
The Alaska Airlines aircraft, which had been in service for just eight weeks, took off from Portland, Oregon.
It was flying at 16,000 feet when the panel tore off the plane.
Pilots flew the jet back to Portland, with only minor injuries among passengers.
The National Transportation Safety Board (NTSB) is investigating if the MAX 9 jet in the Alaska episode was missing or had improperly tightened bolts.
Confidence in Boeing has been shaken since a pair of MAX 8 crashes in 2018 and 2019 killed 346 people and led Congress to pass sweeping reforms for certification of new airplanes.
