Lobbyists who refuse to disclose their clients could be forced to leave the CIPR under new plans expected to be approved later this year.
Senior industry sources told PRWeek that the CIPR was poised to make a crucial amendment to its code of conduct.
The move to encourage greater transparency is expected to be rubber-stamped at the AGM on 15 June and is likely to affect CIPR members including Bell Pottinger Public Affairs chairman Peter Bingle.
The prospect of change to the code follows the recent consultation on a UK-wide 'Public Affairs Council' by the CIPR, PRCA and APPC.
A key purpose of the council would be to promote transparency through a public register of clients.
Following the consultation, the CIPR is considering how to reconcile the plans for a Public Affairs Council with its existing code of conduct, which does not currently require the same level of transparency.
A CIPR spokeswoman said: 'This consultation has now closed and the CIPR is reviewing member comments and the possible implications that CIPR membership of the Public Affairs Council would have for CIPR members.'
One senior lobbyist, keen to see the Public Affairs Council get off the ground, said: 'If everything goes according to plan, the CIPR will have to change its code of conduct. Certain people will then have to take a decision and it is hard to see how it can be fudged.
'In other words, either they declare their clients and stay in the CIPR under the Public Affairs Council umbrella - or they don't declare them, in which case they would be unable to remain CIPR members.'
Bell Pottinger Public Affairs lobbyists would be among those hit by the rule change, owing to the agency's steadfast refusal to disclose its clients on a public register.
When questioned on this by the public administration select committee in March 2008, Bingle defended his stance and cited his team's CIPR membership as evidence of its commitment to ethical practices.
He told MPs his staff were members of the CIPR and therefore adhered to the 'very, very stringent, quite draconian' CIPR code of conduct.