The airport check-in in San francisco was the only place I was asked for papers . Never in Mexico or when we boarded the ship or coming back into Us.Come to think of it Nov 2000 we took a Carnival ship to Couzmel also went to Belize and then I took my daughter on our own to Costa Rica i got a Notarized letter from Ex and i was never asked anywhere to show it . BUt I think it may be better to be safe then denied boarding the ship or plane at the last minute.