That would be one of the exceptions. For example, high-frequency trading firms always need developers on call while they are actively operating. Keeping those s

That would be one of the exceptions. For example, high-frequency trading firms always need developers on call while they are actively operating. Keeping those systems running correctly is essential to their role in the company. Same with small companies who have no other staff, assuming they even have enough employees (15) to be under ADA. :) For the more common scenario of on-call rotation, it would be very difficult to make that argument because other people can take up the disabled person's shifts.