Spirit Airlines’ policy update sparks debate about whether airlines can dictate what passengers wear on flights.

Every airline has a contract of carriage, a legally binding document that flyers agree to abide by while doing business with the airline. These contracts contain language addressing passenger dress, though some are vague ― and very few travelers actually take the time to read them.

Passengers flying Spirit Airlines may need to conceal some tattoos or put on more clothing for their next flight, according to the airline’s updated contract for travelers.