Flying has increasingly become a world of the haves and have-nots, starting with purchasing a ticket and continuing as passengers are sorted by status to board.

Once on the plane, passengers can see where they fit in the hierarchy, with the seats getting smaller and thinner and legroom tighter with each passing row. Then, there’s the scramble to secure space in the overhead bins.

“By the time you walk down the jet bridge, you are a bundle of nerves,” said Henry Harteveldt, founder of Atmosphere Research Group, a travel analysis firm in San Francisco.

Now, some researchers are arguing that the stresses of flying — and they say income inequality is among them — contribute to an increase in unruly behavior on planes.