In 2008, jetBlue partnered with Irish flagship carrier Aer Lingus to allow passengers to switch between airlines on a single ticket for flights with connections in New York–JFK or Boston Logan. Unlike traditional codeshare agreements, the companies cannot sell seats on each other's flights, so customers initiate the purchase on one airline's website and then are transferred to the other site to complete the transaction.
During the last few days of June and the first few days of July 2015, jetBlue began charging for bags in certain booking classes, leaving Southwest Airlines the only major U.S. carrier to not charge for bags. For the classes in which bag check fees are charged (generally the lowest class of fares offered; jetBlue offers 3 classes of fares), the cost is $20 for the first bag and $35 for the second, which is the lowest in the United States besides Frontier Airlines with similar prices.
In January 2010, the airline celebrated its one-millionth passenger to fly out of Phoenix-Mesa Gateway Airport. Allegiant's parent company also announced that it had purchased 18 new MD-80 aircraft from Scandinavian Airlines. In February 2010, Allegiant opened its ninth base at Grand Rapids' Gerald R. Ford International Airport in Michigan. The airline based two McDonnell Douglas MD-80 aircraft in Grand Rapids, but ended their airport's status in 2011. The airline continues to fly out of Grand Rapids in a reduced capacity.
In July 2007, the airline partnered with 20th Century Fox's film The Simpsons Movie to become the "Official Airline of Springfield". In addition a contest was held in which the grand prize would be a trip on JetBlue to Los Angeles to attend the premiere of the film. The airline's website was also redecorated with characters and their favorite jetBlue destinations and the company was taken over by the show/film's businessman villain Montgomery Burns.
For many years, analysts had predicted that jetBlue's growth rate would become unsustainable. Despite this, the airline continued to add planes and routes to the fleet at a brisk pace. In addition in 2006, the IAM (International Association of Machinists) attempted to unionize JetBlue's "ramp service workers", in a move that was described by JetBlue's COO Dave Barger as "pretty hypocritical", as the IAM opposed jetBlue's creation when it was founded as New Air in 1998. The union organizing petition was dismissed by the National Mediation Board because fewer than 35 percent of eligible employees supported an election.
The initial JetExpress partnership with Mesa ended in January 2004, when Horizon Air was selected to operate the routes. Horizon utilized slightly larger CRJ-700 regional jet aircraft on these routes. In August 2006, Frontier and Horizon ended their partnership. While Frontier was generally pleased with Horizon's operation, the carrier decided that it needed to revisit the agreement and find a provider with additional regional jets to grow the operation. The last of the CRJ-700's was returned to the Horizon Air fleet on November 30, 2007.