The call follows the agency's resignation from the Association of Professional Political Consultants after it was found in breach of the body's code of conduct for employing the services of Lord O'Neill (PRWeek, 15 July).
The code states member consultancies must not employ or pay MPs or peers.
Flynn said 'it is inappropriate for organisations such as the Police Federation, Southwark Council, Westminster City Council and The Royal Parks to retain the services of a company that behaves in this manner'.
None of the public sector clients PRWeek spoke to suggested they would take action. Agency MD Charles Lewington said: 'I've written to all our public affairs clients to say we are grateful for their understanding.'