Travelers who don’t check in on time could be unable to check their bags or be forced to miss their flights entirely.

There will soon be another new travel rule that domestic flyers will have to keep in mind before heading to the airport. Starting on June 3, United Airlines will require all domestic passengers to check in for their flights at least 45 minutes before departure.

United Airlines will enforce a stricter check-in deadline for domestic travelers. Passengers must now complete check-in at least 45 minutes before departure, or risk being denied boarding or checked baggage.