United Airlines changes how early you...

United Airlines passengers are facing a big change beginning Tuesday as the airline shifts how early fliers must check-in for trips.

If passengers don’t abide by the new rules, United says, their flight could be canceled.

Effective Tuesday, June 3, United’s “check-in cutoff” for most U.S. flights will be 45 minutes before departure. Luggage also must be checked at least 45 minutes before the flight takes off, United said.

Previously, the cut-off was 30 minutes.

Customers can still use the United app to check in up to 24-hours before their flight, the airline said.

While the new cutoff applies to most of United’s domestic trips, check-in deadlines may vary by location and route. The carrier’s website notes that St. Thomas’ airport in the U.S. Virgin Islands has a check-in time limit of 90 minutes prior to departure — the same cutoff listed for flights between Guam and Honolulu.

For international flights, United requires checking in at least an hour before departure, though many airports have earlier deadlines — such as 75 minutes for major airports in Paris and Dubai, and 90 minutes for the airports in Toronto and Lagos, Nigeria.

MORE: Big changes coming to popular airlines this summer — and they could cost you

In a statement emailed to NBC Chicago, United said the change was made to bring “greater consistency for our customers by aligning with our current checked baggage deadline and the check-in policies followed by most other airlines.”

“If you don’t meet your check-in time limits, we’ll do our best to find another option,” United’s website states. “However, we have the right to deny service which may result in cancellation of your reservation, denied boarding or the option to check your bags.”

The change also comes as amid United’s legal battle with American Airlines over gates at Chicago’s O’Hare International Airport, after the Chicago Department of Aviation awarded United five additional gates, bringing the airline’s total at the airport to 95 starting in October.

According to the CDA, gates are re-allocated basted on how many flights carriers flew into the airport in 2024.

Last month, American Airlines, which has 59 gates at O’Hare, filed a lawsuit against the city of Chicago in an attempt to stop the rival airline, saying the changes “upset the competitive balance at O’Hare.”

Other airlines recently made changes to longstanding polices as the summer travel season begins.

Last month, Southwest Airlines began charging for checked bags – a first in the airline’s history. The move ends the airline’s popular “two bags fly free” perk, charging $35 for a first checked bag and $45 for a second, though there are some exceptions.

Southwest also eliminated it’s popular open seating model and instead started offering “basic economy” tickets.

Passengers on Southwest flights will also soon be required to keep their portable chargers plain sight while using them because of concerns about the growing number of lithium battery fires.