Delta Air Lines and United Airlines have been sued by passengers who claim they were charged extra for a window seat but found themselves sitting next to a blank wall.

The lawsuits, filed separately against the US carriers, seek millions of dollars in damages for more than a million customers of each airline.

They said the companies do not flag that the seats are windowless during the booking process, even when charging a premium for them.

United declined to comment as it was an ongoing legal matter. The BBC has contacted Delta for comment.

The lawsuits, which are similarly worded, seek refunds of extra fees for passengers who said they had paid for window seats but got windowless ones instead.

Both lawsuits, which have been seen by the BBC, were filed by legal firm Greenbaum Olbrantz.

The complaints said some Boeing and Airbus passenger planes had seats that do not have windows because of the positioning of air conditioning ducts, wiring or other components.

These seats are not flagged by Delta and United during the booking process, according to the court documents.

The lawsuits say people buy window seats for various reasons, including addressing a fear of flying and motion sickness, keeping children occupied or for the view.

Some passengers would not have chosen those seats – or paid more for them – if they had known they did not have windows, according to the complaints.

Both airlines describe every seat along the sides of their planes as a “window seat”, even when they know some are not next to a window, the documents said.

Passengers may be charged more to select a window seat compared to a standard seat.

Lawyers representing each case described the practice as “deceptive” and “unlawful”.

Other carriers, like American Airlines and Alaska Airlines, operate similar jets but disclose during the booking process if a seat does not include a window, they added.