While it may sound surprising, it's completely legal for airlines to overbook flights, and, according to Jesse Neugarten, founder of Dollar Flight Club, they do so "all the time." He continues, telling Travel + Leisure, "Airlines are legally allowed to sell more tickets than there are seats on a plane because they know some people won't show up." Think of it as a numbers game based on historical data. "Most of the time, it works out, but every now and then, too many people show up, and someone has to get bumped."
The somewhat hidden clue is in the sequence number, or simply "SEQ" on a boarding pass, which references the order in which passengers can check in for a flight. That order can then be used to determine who is able to board a flight, and who is not. In fact, that same sequence number can be used to determine whether a passenger gets involuntarily bumped from a flight, according to the U.S. Department of Transportation (DOT).
Under Canada's Air Passenger Protection Regulations (APPR), if your flight is cancelled due to a labour disruption, airlines must offer you a choice between a cash refund or a rebooked flight.
"Many crew members and avid cruisers can tell you about seeing 'pier runners' sprinting down the dock only to watch in horror as their ship pulls up its gangway and sails off into the sunset without them."