Interference by the IRS

A new client found himself in a quandary.  His customer owed him over $100,000. What was the reason for not paying?  The client had a $75,000 tax lien from the IRS and the IRS had levied on the customer, prohibiting the customer from paying the client.  The customer was happy not having to pay either the client or the IRS and the IRS was happy to do nothing, except possibly to find another customer of our client to sock with a levy.  What could the client do to get the money from the customer to satisfy the IRS lien ?  We filed a collection action against the customer in State court, joining the IRS as a party, and attached to the complaint IRS form 2848, duly signed by the client and filed with the IRS, giving the IRS authorization to recognize our law firm as an authorized representative.  The complaint noted that the IRS was joined to protect its interest, if any. The IRS has a special office to receive service of such actions.  For those interested in the welfare of our law firm, the action also cited appellate law that our interest in our usual 25% contingent fee is paramount to the IRS lien.  So moves a rock from a hard place.