Airlines are letting flyers change their trips ahead of a major winter storm that will put carriers to the test during one of the busiest travel periods of the year.

A winter storm warning is in effect starting this afternoon in New York City, New Jersey and Long Island, with snowfall totals potentially reaching 9 inches, most of it falling overnight, the National Weather Service said.

American Airlines, Delta Air Lines, United Airlines, Southwest Airlines, JetBlue Airways and other carriers waived change fees for restrictive basic economy tickets and said they won’t charge a difference in fare for customers flying in and out of several airports in the area, including at Philadelphia International Airport, New York’s John F. Kennedy International Airport and Newark Liberty International Airport in New Jersey.

Customers must travel by the end of the year if they change their flights, the airlines said. Flying as early as possible is likely the best bet with few seats available during the busy Christmas week.

Airlines for America, the industry lobbying group, expects carriers to fly a record 52.6 million people between Dec. 19 and Jan. 5, with this Friday and Sunday among the busiest days.