Is it possible to block certain user groups from being added as Approvers or Acknowledgers

Hi,

We have Department User Groups, and we have Approval Groups that are department oriented.

The Department Groups hold more people than the Approval Group for that department, as not all people are allowed to be Approvers/Acknowlegers.

I have tried creating a criteria that dose not allow the Department Groups to be listed as Approvers/Acknowledgers, but this only allows Names to be added, and not Groups.

Does anyone know if it is possible to block certain User Groups from being added to Changes?

Or, if they are added, stop progress?

Thanks for any help.

Alan