The industry stance, which emerged this week in a report published by Ofcom's Office of the Adjudicator, demands that CRR be kept in place beyond the current 2006 timetable.
The IPA said that CRR is "essential to maintaining an equitable position in dealings with ITV plc", while ISBA said that it provided "an effective safeguard for its members against ITV plc's potentially powerful market position".
Charles Allen, ITV's chief executive, has called for CRR, which could cost the broadcaster between £120 million and £150 million in this year's annual round of airtime trading deals, to be ended.
ITV is in a deep-seated ratings slump and under the terms of CRR, advertisers can reduce their commitment pro rata without penalty.
The adjudicator, the former Starcom director David Connolly, also reveals that media agencies have expressed concerns that ITV is engaged in "overt conditional selling" in an attempt to bring in revenues for its digital channels.
The report also criticises ITV for failing to finalise draft contracts with advertisers and media agencies, though ITV blames agencies' reluctance to sign.