First tell the Revenue Officer (“RO”) that you must contact your client to discuss whatever the new issue is that he or she has brought to your attention.  Assuming your client has not paid you for the new work (a promise to pay is not enough), call the RO back and indicate that you have not been paid and therefore are not representing the taxpayer until the retainer is received.  Tell your client that you informed the RO that work has stopped until you are paid.  If your client is serious about resolving the new issue, they will find a way to pay you.  If not you can revoke your Power of Attorney.