The trade group Airlines for America is predicting record numbers of airline passengers this summer, but travellers may face long lines and increased flight delays and cancellations, Bloomberg reports.

With an average of 2.8 million people flying each day in the US, the worldwide grounding of the B737 Max jet fleet due to safety concerns could result in a shortage of aircraft to handle the crowds.

American Airlines, United Airlines and Southwest Airlines have already removed all flights slated to fly the troubled aircraft from their schedules until August. Industry experts still cannot say when the B737 Max, involved in two recent fatal crashes related to onboard computer problems, will be cleared to fly again.

Separately, the Trump administration’s decision to reassign airport security personnel to work at the Mexico-US border could cause longer queues at checkpoints.

“As the busy summer travel begins, it couldn’t be a worse time [to] undermine important safety programmes and endanger the safety, security and comfort of the travelling public,” said Sara Nelson, the president of the Association of Flight Attendants-CWA.