14 CFR § 382.77 - May carriers restrict the location and placement of service animals on aircraft?
(a) You must permit a service animal to accompany a passenger with a disability on the passenger's lap or in the passenger's foot space, unless this location and placement would:
(2) Encroach into another passenger's space.
(b) Before refusing to transport a large service animal that cannot be accommodated on the passenger's lap or in the passenger's foot space without encroaching into another passenger's space, you must offer the passenger the opportunity to move with the animal to another seat location within the same class of service, if available on the aircraft, where the animal can be accommodated. You are not required to reseat other passengers to accommodate a service animal except as required for designated priority seats in Subpart F.
(c) If there are no alternatives available to enable the passenger to travel with the service animal in the cabin of the scheduled flight, you must offer the passenger the opportunity to transport the service animal in the cargo hold free of charge or travel on a later flight to the extent there is space available on a later flight and the transport is consistent with the safety requirements set by the FAA or a foreign carrier's government.