It’s not news that airlines have been squeezing more — and smaller — seats into the backs of their planes. The question is how far they can push their quest for higher profits before running into a backlash from their customers.

“The commercial side — primarily the people who run airline revenue departments — want more seats on planes,” said Henry Harteveldt, co-founder of Atmosphere Research Group, an airline and travel industry analyst. They’re up against “the people in the airlines’ marketing departments, who are trying to act as their passengers’ advocates and push back on some of these initiatives.” ...