United Airlines has banned certain types of dogs from traveling the friendly skies and published the list on it's website. Previous to this, United did not have any pet restrictions.
The ban includes Pit Bull Terriers, American Staffordshire Terriers, Presa Canario, Perro de Presa Canario, Dogo Argentino, Cane Corso, Fila Brasileiro, Tosa (or Tosa Ken) and Ca de Bou that are either six month or older or are 20 pounds or heavier.
In placing the ban, the airline said they are adopting Continental's "PetSafe Program", which is considered a superior product because it has its own travel desk and resources stations across the country. United and Continental recently merged into one airline.
Continental's PetSafe program had those restrictions and that is where the new ban is coming from said airline officials.
Though United is the only airline with a ban on certain breeds, all airlines have said they reserve the right to deny transport to any animal they deem dangerous.
United also recently modified is classification of pets as "cargo" because service members returning home from overseas deployments and other passengers were incurring significant fees by third party handlers who coordinate cargo for the airline. It now classifies pets traveling with passengers as baggage, however unaccompanied pets are still considered cargo.