One of pet-travel lover Aliza Bodzin shared her experience:
It is recommended to choose United Airlines for travel to and from Spain if you are based in the United States of America.
The process of adding a pet in the cabin to a reservation with United Airlines is straightforward, and their maximum carrier size exceeds that of Iberia Airlines. Furthermore, United Airlines offers daily flights from EWR and IAD to MAD and BCN.
On a positive note, Iberia Airlines does allow pets in the cabin in their business class.
I personally travel to and from Spain annually and avoid flying with Iberia when accompanied by my dogs, unless there are no other viable options. Last year, we paid a premium for our United Airlines tickets to avoid the stress associated with adding a pet to Iberia Airlines' reservation.
To add a pet to an Iberia Airlines reservation for in-cabin travel, you are required to contact their customer service in Madrid because their US-based service is nearly non-existent.
To circumvent international surcharges when contacting Iberia Airlines by phone (I made the mistake once, incurring $200 in fees), I sent my phone number via direct message to Iberia's Twitter (X) account, allowing their customer support team in Madrid to reach out to me.
We typically stay in Madrid before taking the AVE train to our homes in the south. We prefer the comfort and convenience that AVE offers when traveling with our dogs, as opposed to Iberia-Vueling.