United, Continental, American and Delta all have summer pet plans, particularly relating to snub-nosed breeds. We recently offered an overview of pet travel during the summer, and always advise choosing a pet-friendly airline that won't leave pets out on the tarmac.
Even with these rules in place, scorching temperatures like the ones we're experiencing this week make changes possible at any time. For example, today (Thursday) Continental has decided they'll only be flying pets before 10 a.m. and after 8 p.m. from Chicago O'Hare, and from today through Saturday pets will be flown before noon and after 8 p.m. from Newark Liberty International Airport.
Changes like these are often made and there may be more to come, so it's important to double check flight information before you leave home. Also, be sure to stay in touch with news sources like PetRelocation.com!