As customers face hours-long phone waits for customer service, Delta Air Lines has called some former reservations employees back to work on a temporary basis to help handle the load.

Delta’s reservations lines are overloaded as travelers return to the skies and seek to use credits from flights canceled early in the pandemic. That means some customers faced phone waits of more than five and a half hours on Tuesday, for example.

Atlanta-based Delta cut about 18,000 people from its staff of 90,000 as travel dropped 60% in 2020 due to COVID-19, and had more than 40,000 employees take voluntary unpaid leaves of absence last year.

Today, the company has about 75,000 employees, but some are still on leave. According to the most recent federal statistics, Delta had 65,659 employees working in April, including full-time and part-time workers. That’s down 27% from a year earlier.

The airline is now increasing its staffing levels as the summer travel season ramps up, bringing back hundreds of reservations agents who have worked for the airline in the past because they have the skills to quickly begin handling calls again.

Delta has already seen a strong recovery in domestic leisure travel this month, driving more queries from travelers. The long waits mark a return to some of the frustrations from last year, when travelers waited for hours to cancel flights and seek credits or refunds as the coronavirus spread.

The company in a written statement Tuesday acknowledged that “our wait times are not currently where we’d like them to be,” and apologized to customers.

“We are seeing a higher call volume as more customers are beginning to travel, so we’re adding staffing through more scheduled hours and overtime for our specialists, hiring temporary summer contract workers and fast-tracking technology upgrades to reinforce existing self-service options to assist with travel needs,” Delta said. The airline also plans to hire 1,300 new employees this year to help handle the workload.

Delta recommends customers first try using the airline’s online tools to rebook or change flights or find out about travel requirements.