United Airlines is asking its pilots to take time off in May because of delays in receiving new planes that the airline ordered from Boeing, which is struggling with production due to manufacturing problems.

A United spokesperson said Monday that the offer is voluntary.

“Due to the recent delays in Boeing deliveries, our forecasted (flight hours) have been reduced and we are offering our pilots voluntary programs for the month of May to reduce excess staffing,” spokesperson Leslie Scott said.

Neither the pilots’ union nor Boeing commented immediately.

United hasn’t received as many Boeing 737 Max and 787 Dreamliner planes as it expected. Federal regulators are investigating production quality issues at Boeing that have delayed aircraft deliveries and pushed back the launch of a new, larger Max model that United expected to begin using this year. United is considering options to replace orders for the new Max 10.

CEO Scott Kirby is one of several airline CEOs who have called out problems at Boeing and sought a meeting with Boeing directors.

Boeing announced last week that CEO David Calhoun will step down at the end of the year as part of a leadership shakeup at the company. The head of Boeing’s commercial-airplanes unit has already been replaced, and the chairman of the board will not stand for re-election in May.

(AP)