American Airlines is planning to run an anti-vaccination message from the Australian Vaccination Network, AVN. AVN is a mis-leadingly named organization that promotes the discredited link between vaccines and autism, among other anti-scientific nonsense. They claim there is scientific debate about the dangers of vaccines (there is no such debate) and also claim  that vaccines don’t work anyway, as evidenced by the rising rates of measles and whooping cough (these outbreaks have been overwhelmingly, >85%, linked to UNVACCINATED individuals ).
A petition has been created, with a goal of 1500 signatories. The petition explains why this is a dangerous and irresponsible message to air on an intentional airline, and offers you the chance to sign so your voice is heard. I also recommend you send your own mail to American Airlines customer relations.