Sure. I just realize that so many people have been underpaid for no good reason, whether due to negotiating inexperience or discrimination or simply coming from a different geography or the nonprofit sector, that requiring pay history is not something I can support as a routine requirement.

Verifying any pay history info that is provided, however, seems fine to me. This could certainly be via pay stub, or it could be by contacting the former employer with candidate consent after the official offer letter is issued and accepted (worded to be revocable if the verification fails).