Twenty-one airlines are being relocated at LAX in what airport officials are calling one of the largest terminal moves in the history of commercial aviation. The changes are a result of the Delta Air Lines move from Terminals 5 and 6 to Terminals 2 and 3 at Los Angeles International Airport. Delta’s relocation to the north side of the U-shaped airport is part of the huge modernization effort at the nation’s second busiest airport.

The move affects nearly one-third of the airlines that operate out of LAX, with many moving to new terminals and others to new ticket counters within their current terminal. The airlines plan to complete their relocations overnight, opening the next morning in their new spots, Los Angeles World Airports said in a news release, describing the effort as “a move of airlines never before seen at a major U.S. airport.”