(CBS) — Alaska Airlines is apologizing, after a straight couple got preferential treatment over a gay couple when a seat on a New York-to-Los Angeles flight was double-booked.

David Cooley said a flight attendant asked his traveling companion to give up his premium seat on Sunday, so another couple could sit together.

When Cooley and his companion explained they were a couple and also wanted to sit together, his companion was told to either give up his premium seat and move to coach, or get off the plane.

Cooley said he and his companion chose to leave, because they felt humiliated, and will never fly Alaska Airlines again.

“We could not bear the feeling of humiliation for an entire cross-country flight and left the plane. I cannot believe that an airline in this day and age would give a straight couple preferential treatment over a gay couple and go so far as to ask us to leave,” he wrote in a Facebook post.

Alaska Airlines has issued a statement in response to the incident:

“We mistakenly booked two people in one seat. We are deeply sorry for the situation, and are investigating the details.”

The airline added that it has a zero-tolerance policy for discrimination of any kind.