New York(CNN Business) United Airlines now plans to cancel all flights involving Boeing 737 Max planes until August — a month longer than previously announced.

The airline expects to cancel roughly 2,400 flights in June and July, a large chunk of the busy summer travel season.

"We won't put our customers and employees on that plane until regulators make their own independent assessment that it is safe to do so," United said in a statement. The company added that it will continue trying to automatically rebook affected customers on other flights.

United said in April that it would cancel all flights through "early July" because of the Boeing 737 Max grounding. The latest extension is through August 3.

The airline joins other US carriers — American and Southwest — that have canceled 737 Max flights until sometime in August. Boeing's Max planes were taken out of the skies in March after a 737 Max jet flown by Ethiopian Airlines pilots crashed in that country, killing everyone aboard. It was the second fatal crash involving a Max in recent months. A total of 346 people died in the two crashes.

It's still not clear when authorities will allow the plane to fly again.

Daniel Elwell, the acting administrator of the Federal Aviation Administration, said this week that the agency has not committed to any timeline to recertify the Max, even though some airlines have expressed hopes the flight restriction would be lifted by August.

Scrutiny remains on the FAA for its prior certification of the aircraft and its software system designed to push the nose of the airplane down if it senses an imminent stall and is believed to have played a role in both crashes.

The FAA met with delegates from 33 international aviation authorities Thursday in Fort Worth, Texas, to discuss processes for reviewing the software fix Boeing has completed for the aircraft, which remains grounded worldwide.

Boeing (BA) did not immediately respond to a request for comment.

United (UAL) has been forced to cancel roughly 30-40 flights per day while regulators continue to investigate whether the aircraft is safe to fly. United doesn't fly any Max 8 jets, the type of plane that was involved in both of the fatal incidents. But it does have 14 Max 9s, which are a slightly longer version of the Max 8.

Other US airlines have even more Max planes in their fleets. Southwest (LUV), which flies 34 Max jets, has already canceled all Max flights through August 5. American (AAL), which has 24 of the planes, said last month it would cancel about 115 daily flights through August 19.