Written with people moving from Turkey in mind. The Portuguese rules still apply more broadly.
Pets on Trains and Metro
You can take pets on public transport in Portugal, usually for free. Small pets must travel in a carrier. Larger dogs are allowed but must be on a short leash and wear a muzzle (açaime), regardless of the breed.
You must also carry the pet's vaccination bulletin and registration document. Conductors can refuse entry if the train is too crowded or if the animal appears aggressive or dirty.