ASSOCIATED PRESS An employee in Delta’s operations control center sent a directive to a Delta gate agent directing them not to open the door of a delayed flight in order to keep the flight attendants onboard, according to internal communications reviewed by HuffPost.

A recent Delta flight leaving Atlanta ran into a maintenance problem, causing a lengthy delay before takeoff. As the airline tried to resolve the issue, someone feared the holdup might cause an even bigger headache: flight attendants walking off the plane because they had worked so long.

So, according to internal communications reviewed by HuffPost, an employee in Delta’s operations control center sent a directive to the Delta gate agent handling the flight.

“Do not open door,” the message read. “flt attendants out of time and none available.” The employee advised the gate agent to “let [maintenance] do their work without opening door thanks.”

Whoever sent the message seems to have been worried that the flight attendants would soon hit their maximum duty hours ― the most they can be required to work continuously without a break. And that, tired and annoyed, they would walk off the plane, forcing the airline to scramble to find another crew, or cancel the flight.

Flight attendant duty-hour rules vary from airline to airline. Generally, once an attendant hits the maximum hours for a series of flights, they can’t be forced to continue on the next segment, although they would get extra pay if they do. It isn’t clear whether these attendants would have had the option of leaving the plane in this particular situation, but someone in operations control apparently believed they did.

The message above went out at 10:19 p.m. About a half-hour later, the operations center sent an even more urgent note: “Ok… if door is not closed by [11 p.m.] Flt attendants walking. We will most likely have to delay flight until morning if this happens.”

Someone in the flight tower responded, “Copy.”

The correspondence suggests the flight in question was Delta 1990, going from Atlanta to Toronto, on May 12. Flight history from the airline tracking site FlightAware.com shows the flight left nearly three and a half hours after it was scheduled to, at 11:27 p.m. It got to Toronto a little after 1:30 a.m.