At a time of heightened security concerns, disgruntled airline employees and frustrated passengers can be a combustible combination in a crowded aircraft, as travelers find themselves subject to lots of rules and little wiggle room to challenge them.

On a United Airlines flight from Zurich to Washington Dulles International Airport on Jan. 2, Bill Pollock asked a flight attendant about a sign telling passengers not to venture beyond the curtain separating economy class from the rest of the plane. Mr. Pollock, a book publisher from Burlingame, Calif., said he wanted to stretch his legs and visit his wife seated on the opposite aisle, using the passageway behind the galleys in the plane's midsection.