When one passenger was denied that bit of personal space Sunday, it led to a heated argument and the unscheduled landing of their plane.

Airline passengers have come to expect a tiny escape from the confined space of today's packed planes: the ability to recline their seat a few inches.

The fight started on a United Airlines flight because one passenger was using the Knee Defender, a $21.95 gadget that attaches to a passenger's tray table and prevents the person in front of them from reclining. United Airlines said it prohibits use of the device, like all major U.S. airlines.

The dispute on United Flight 1462 from Newark, New Jersey, to Denver escalated to the point where the airline decided to divert to Chicago's O'Hare International Airport, according to Transportation Security Administration spokesman Ross Feinstein.

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Chicago police and Transportation Security Administration officers met the flight, spoke to the passengers — a man and a woman, both 48 — and "deemed it a customer service issue," Feinstein said.