The following article refers to functionality in Workflow Builder, which can be found by going to:
Administration > HR > Workflows
This option allows you to trigger workflows against employees with a manager level job role only. This can be used to restrict a workflow so that it only triggers against such employees.
When building or editing a workflow, the option can be found towards the bottom of the screen, labelled 'Only manager roles?'
PLEASE NOTE -
This does not relate to an employee's user group, only their job role, so it would not trigger against a user with a Manager user group unless they also had a manager-level job role.