Drivers may choose to stop receiving Uber Pet trips requests at any time, but are still required by law to accept riders with assistance animals (e.g. guide dogs) – assistance animals are legally allowed to go everywhere their owner goes. - Uber AU Pets policy
Riders with service animals are not required to use Uber Pet. Per Uber’s US Service Animal Policy (see below), driver partners have a legal obligation to provide service to riders with service animals, regardless of ride type. Uber US Pets policy
Uber Pets also charges a premium, which would still be discrimination in these cases. This is likely why people with assistance animals are not required to select it.