When creating Service Level Agreements (SLAs) it may not be possible to select some Organizational Units.
This KB article has a possible explanation of why this may occur.
It is only possible to select the Organizational Unit that the logged in User belongs to or ones that are below their Organizational Unit in the hierarchy. It is not possible to create a SLA for an Organizational Unit that the logged in user has no connection to.
If an Employee record is linked to the "Professional Services" Organizational Unit:
They can only create SLA's for the Organizational Units: Professional Services, Consulting Services and Educational Services