I left out some details, it wasn’t only payroll, there was some other staff management aspects to it. But overall the answer about using ADP for this particular situation is: no.

Not strictly for technical reasons, but definitely for political reasons. The client was potentially the largest organization in my province (state-run healthcare). Outsourcing payroll and scheduling with the potential of breaking the rules in the contracts with the multiple union stakeholders was a completely non-starter. Plus the idea of needing to do lay offs within the payroll department was pretty unpalatable.