New Activity Alert

Hi all - 

I have a requirement from a user that whenever an activity is created (Phone Call, Appointment, Email) in CRM, then an email alert should be sent about it. 

However, the alert should only be sent if the Account record associated with the activity meets a certain criteria (account has a field called 'new_category' - category must be 'Law Firm').

I am able to achieve this through a workflow when the Regarding of the activity is the Account record, as I can directly query the 'new_category' field in the workflow. However, I need to also achieve this if the Regarding is a contact - I cannot query the contact's parent account attributes in the workflow.

Any suggestions of how to achieve this?

Thanks,

Rich