Do we need CRM license for integration with internal ERP application

Hi,

we have ERP application and there are users from back-office operations who updates account and contact records in this applications.

Account and Contact entities are integrated between CRM and ERP.

There are 10 salespersons who works only with CRM application.

Do we need somehow license back-office users in such scenario. Or it is enough to have 10 user CALs and server license.

thanks!