NEW YORK — Stragglers beware: U.S. travelers flying with United Airlines will have to check in to domestic flights a little earlier starting next week. That is, if they’re customers only taking carry-on bags.

Effective June 3, United’s “check-in cutoff” for most U.S. flights will be 45 minutes before departure. That’s the same deadline United has for passengers checking luggage at the airport but 15 minutes earlier than the current one for people without bags to check.

In an email to The Associated Press, a United spokesperson said the change to a single cut-off minimum “brings greater consistency for our customers” and conforms with the policies of many other airlines.

Checking in for a flight confirms a passenger’s booking and intent to travel ahead of takeoff. Most major U.S. carriers have online check-in systems that can be used at least 24 hours in advance, so the process no longer reflects when many travelers arrive at the airport. But it’s still an important step since boarding passes are issued once check-ins are completed.

Other U.S. and international carriers have tightened their check-in and boarding policies as part of their strategies for maintaining on-time departures, particularly amid the high demand that followed the COVID-19 pandemic.

Generally speaking, checking in allows airports and airlines to prepare for upcoming flights — from confirming seat assignments to making sure passenger names are at the security checkpoint. Check-in cutoffs, or the latest possible time to claim a flight reservation, are typically earlier for international flights to account for the time needed to check passports and clear customs.

Still, requirements may vary by airline and airport. Dubai-based Emirates, for example, closes online check-ins 90 minutes before departure. Ireland’s Ryanair allows online check-in up to two hours before a flight; passengers still may check in at the airport 40 minutes in advance, but for a fee.

Here’s what check-in cutoffs look like for United and some other U.S. carriers.

Again, if you’re flying United within the U.S., you’ll need to check in to your flight at least 45 minutes prior to takeoff as of June 3.

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. But 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.

Delta passengers not checking any bags still have a minimum of a half-hour before a domestic flight to check in. Travelers with luggage to check need to get to the airline ticket counter at least 45 minutes prior, Delta’s website notes, per an update that went into effect last month.

In a statement sent to the AP on Tuesday, Delta said it had made this “minor change” so that “Delta teams can ensure all customers have a great experience.”

For international flights, Delta travelers must be checked in at least 1 hour before departure. But, like other carriers, Delta’s minimum check-in requirements can vary by location for certain airports. Delta customers checking bags at New York’s John F. Kennedy International Airport, for example, are supposed to check in an hour before departure whether their flights are domestic or international.

If you’re flying with American Airlines within the U.S., the deadline for checking in and checking a bag before a flight is 45 minutes ahead of departure, according to the carrier’s website.

For trips to or from locations outside the U.S., the cutoff to both check-in for your flight and check a bag is 60 minutes ahead of takeoff. But again, a handful of airports have earlier requirements.

Passengers with more than a carry-on bag should get to the airline counter at least 45 minutes before a scheduled flight on Southwest. The carrier warns that baggage destined for a plane’s cargo hold is considered a “late check” and not guaranteed to get on your flight if it’s dropped off less than 45 minutes ahead of departure.

Beyond baggage, if Southwest travelers aren’t checked-in and in the boarding area at least 10 minutes prior to departure, their reservation could be canceled, a Southwest spokesperson told the AP via email.

The carrier did not specify any additional, firm check-in cutoffs for domestic flights. For international trips, Southwest’s website notes that all passengers and their luggage must be checked in a minimum of 60 minutes prior to departure. And again, that can vary — with flights departing Aruba, for example, having an earlier deadline of 75 minutes before takeoff for passengers with or without checked bags.

Alaska requires a minimum of 50 minutes before takeoff to check in passengers for flights within the U.S., whether or not they have bags to check. The cutoff is 60 minutes for international flights, the carrier’s website notes.

Again, there are exceptions for certain locations and airports. Passengers traveling from Guadalajara, Mexico, for example, have to check their baggage and into their flights at least 90 minutes ahead of time.