Originally Posted by
mduell
First things first, the airline can choose to reseat you at any time for any reason or no reason at all. Doesn't matter if or how much you paid, how long you held the seat assignment, etc. They make this very clear in the CoC you agree to when you buy the ticket.
The only regulation I'm able to find relating to compliance with crewmember instructions is specifically with regard to smoking and seatbelts:
[I]§ 121.571 Briefing passengers before takeoff.
Not a regulation, but UA's Contract of Carriage says that they can refuse to transport: "Passengers who fail to comply with or interfere with the duties of the members of the flight crew, federal regulations, or security directives;"
Which seems like a catch-all they can use for any refusal to follow FA's instructions if they want.