Delta Air Lines and United Airlines were sued on Tuesday by passengers who claimed they paid extra money to sit in “window” seats, only to find themselves placed in seats next to a blank wall.

On these types of aircraft (as well as several others), the cabin window lines are interrupted by the existence of air conditioning riser ducts, window conduits, or electrical wiring embedded in the cabin wall, which makes placing a window there impossible for the manufacturers.

United and Delta Airlines are being sued by passengers who say they paid extra for window seats — only to be seated next to a barren wall during their flight. The proposed class action lawsuits, filed in federal courts Tuesday seek millions of dollars in damages for over one million customers who rode on each airline.