Lufthansa, the German national airline, is suing a passenger for missing his layover. This story is a little more complicated than an airline suing a customer for being late or careless: Lufthansa is claiming that the passenger booked a flight from Seattle to Oslo, Norway, with a layover in Frankfurt, Germany, and intentionally missed the connecting flight, instead boarding a different Lufthansa flight he had booked that was headed to Berlin, his intended destination. (Would he have gotten caught if he had just, you know, booked the Berlin flight through a separate airline? Who knows.)

The passenger, who is unnamed in court documents obtained by CNN, was allegedly taking advantage of a loophole that makes fares through a certain destination — such as a flight to Oslo through Frankfurt — cheaper than fares to that destination. Lufthansa is claiming €2,112 (approximately $2,300) in damages, claiming the passenger violated its terms and conditions by using the so-called “hidden city” loophole.

Here’s how it works: Let’s say you need to get from point A to point B, but for some reason, it’s cheaper for you to fly from point A to point C with a layover in point B. As long as you don’t check a bag (since checked bags always fly to the plane’s final destination, provided the airline doesn’t lose your luggage) there’s theoretically nothing stopping you from simply not catching your connecting flight, as long as your paperwork is in order.

These flights are cheaper because, as the blog Cranky Flier points out, “airlines don’t price based on cost. Airlines price based on demand.” A direct flight is more desirable than a flight with a layover, so airlines will price those flights higher. And certain cities, like Frankfurt, also operate as hubs that serve as common layover points. An airline can fill a plane into Frankfurt with a mix of customers who are actually headed there and others who are stopping there to catch a flight elsewhere.

Airlines, obviously, don’t like that people have caught on to hidden city ticketing. The most obvious reason is that if someone books a flight and only shows up for one leg of it, the airline can’t sell that seat to another passenger. (Although it’s worth noting that airlines often overbook flights, and it’s always possible that someone is waiting to catch a flight on standby — but since it’s not a guaranteed sell, airlines don’t prefer it.)

They also claim that passengers who intentionally miss part of their flight make things worse for other customers: Gate agents could hold the flight for a passenger who has no intention of showing up, possibly delaying the flight and having a cascading effect. And a customer who purchases a flight he has no intention of taking could drive prices up for other customers who try to book later by making it seem like there’s more demand for that flight than there actually is.

Airlines also argue that the hub-and-spoke model, where one airport serves as a “hub” to other airlines in the region, lets them keep prices low in order to compete with budget airlines, which do charge per leg.

The Lufthansa lawsuit isn’t the first time an airline has sued someone for gaming the system. In 2014, United Airlines and the booking website Orbitz filed a joint suit against Aktarer Zaman, the then-22-year-old coder behind Skiplagged, a website that helps people find hidden city flights, claiming $75,000 in damages. United argued that Zaman was unfairly competing with other booking sites and promoting “strictly prohibited” travel. Orbitz joined the suit because Skiplagged redirected potential passengers through Orbitz, effectively forcing the site to violate its own contract with United. A judge ended up throwing out the case because it was filed in Chicago and Zaman neither lived nor worked in that jurisdiction.

As for the Lufthansa suit, it’s unclear what will happen next. A judge dismissed the case in December, but a Lufthansa spokesperson told CNN that the company “has already filed the appeal against the decision” and will move forward with the case. One travel blogger argues that no matter the outcome, Lufthansa will end up looking like the bad guy. After all, it’s rare that the public will side with an airline.