Originally Posted by
bbtrvl
This is an airline requirement. If you do not provide passport info 72 hours before departure, or at time of booking when booking within 72 hours, then the airline reserves the choice to deny you check-in or boarding.
As it's up to the airline, you can expect that the enforcement will probably vary a lot between airlines, airports, and maybe even check-in agents.
Every major alliance carrier to the US flies lots of passengers on flights booked 2-24 hours in advance of travel, and the 72 hour thing alone doesn't result in the scare-mongering outcomes people put up about such travels.