Two passengers leave the plane on an emergency sleigh before take off from New York City

The airline said two passengers opened the cabin door on a Delta Air flight, and escaped an emergency slide shortly before take-off Monday at LaGuardia Airport.

The passengers, who have not been identified, were on a flight bound for Atlanta when they opened the cabin door.

The statement said the Airbus A321 aircraft was in operation at the time and returned to the gate. The airline said other passengers had been placed on alternate flights.

The company said maintenance crews have evaluated the plane and is scheduled to return to service on Monday.

It was not immediately clear what caused the speedy exit. The Police Department at the Port Authority of New York and New Jersey, which runs the airport, did not immediately respond to a request for comment.

The New York Times, citing another passenger on the plane, identified the couple as a couple with a service dog who had switched seats multiple times before takeoff.

The passenger, Brian Plummer, said the man stood as the plane began to move and ignored the flight attendant’s order to sit down.

Plummer told The Times that he had not seen the man open the cabin door, but that the cabin crew alerted the passengers after the plane suddenly stopped.

The newspaper reported that after the man was forced to open the emergency exit, the couple left with their dog.