American Airlines Group Inc. dropped about 1% of its scheduled daily flights for July after a faster-than-expected surge in summer travel led to crew shortages.

The airline will cancel 950 flights during the first 13 days of July, after it scrapped more than 400 flights over the weekend and into Monday on what it cited as poor weather conditions at its Miami and Chicago hubs that exacerbated a shortfall in pilots. In some cases, delays caused by storms exhausted its group of reserve pilots.

The sudden jump in demand fueled by people tired of staying close to home has strained airlines’ ability to rebuild operations cut back amid the onset of the pandemic last year. Pilots who took leave and those who were switched to new types of planes have had to be retrained as flight demand has recovered to near-2019 levels.

American added flights back faster than its primary competitors and is operating at about 10% below its 2019 seat capacity, according to records from flight-data firm OAG. Delta Air Lines Inc. is more than 20% behind pre-pandemic capacity and United Airlines Holdings Inc. is more than 30% below. American didn’t immediately comment on the difference.

American and other airlines have had trouble matching their desire to offer flights with their ability to assemble crews, although it expects to complete training for furloughed pilots by the end of June. The airline said it dropped flights in markets that have other options for passengers and is working to make schedule changes in advance of travelers’ departure dates.

American rose 0.5% to $22.41 at 2:47 p.m. in New York trading, the smallest gain on a Standard & Poor’s index of the five largest U.S. carriers, which rose 1.4%.

Southwest Airlines Co. canceled about 200 flights Monday—the most among U.S. carriers, according to tracker FlightAware.com—and 30 more on Tuesday ahead of summer storms that were expected to push across much of the U.S. South and Northeast, including the New York City area, Washington and Philadelphia, a spokesman said. About 480 Southwest flights, or 13%, were delayed Monday, FlightAware data showed, followed by 12% at American.

U.S. carriers have struggled to match the supply of aircraft and crews with soaring demand for air travel. The seven-day average number of passengers exceeded 1.9 million for the first time since the pandemic, according to Transportation Security Administration tallies of people going though security at U.S. airports.

While raw passenger counts have been climbing steadily as infections and deaths fall, the trend coincides with the traditional increase as the summer travel season approaches. As a result, the number of people flying has remained at about 73% of 2019 levels, including for all of June.

“We’re just seeing a rocket ship straight up to where we were prior to the pandemic domestically,” said Dennis Tajer, an American captain and spokesman for the Allied Pilots Association. About 1,000 American pilots retired early or left the airline voluntarily during the pandemic as U.S. carriers sought to reduce headcount to match gutted demand.

American’s scheduling system, which has long been a sore point between the carrier and its pilots union, hasn’t kept up with the expanded schedule, he said. “We’re disappointed that management is surrendering to reducing the schedule rather than working with APA to create solutions to fly the schedule.”

Aviators who have been concerned about American’s viability have encouraged the airline to “be aggressive” with allowing willing pilots to pick up overtime flying, Tajer said.

The airline didn’t immediately comment on the union’s claim.