i have a workflow that is supposed to update a field that is a list/record of department based on another field which is list/record of employees. the issue is that the users are getting an error: reference key ERROR: Field Is Restricted. Which permission is required to have the field not be restricted?

Are these both custom fields?

Yes. This is on a custom record.

Are there any restrictions or permission set directly on the Field Config?

Negative. No permissions set. Looking into it some more I believe it may be a subsidiary thing but the custom record does not have a subsidiary field.

i think they need at least View permission for Department and Employee Record

i had the department field source from the field that is a list/record of employees and that is working so am thinking it is a permission issue when doing it via workflow.

or check the run as administrator box on the workflow

Execute as admin worked! Thanks!