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

The fight started on a Denver-bound United Airlines flight because one passenger in the economy-plus seating 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.

The Federal Aviation Administration leaves it up to individual airlines to set rules about the device. United said it prohibits use of the device, like all major U.S. airlines.

The dispute on Flight 1462 from Newark, N.J., escalated to the point where the plane decided to divert to Chicago’s O’Hare International Airport, according to Transportation Security Administration spokesman Ross Feinstein.

Chicago police and TSA officers met the flight, spoke to the passengers — a man and a woman, both 48 — and “deemed it a customer service issue,” Feinstein said.

The plane then continued to Denver without them, arriving 1 hour and 38 minutes late, according to the airline’s website.