The Periodical Publishers Association (PPA) claims the plans, which, if approved, would come into force from October 2003, would "wipe out" A3 weekly news-based tabloid magazines, especially in the business-to-business (B2B) sector.

The Royal Mail could increase postal costs by 50- 150%, or as much as 1.2m a year for a single title, the PPA added. It also said that while publishers with a mixed portfolio of A3 and A4 would face a neutral outcome, this ignores that magazines are often treated as individual profit centres.

The other option put to publishers is based on amendments to the Royal Mails current model.

PPA director of circulation Nicola Rowe said the Royal Mail wanted to "maximise the machinability of mail", but added that magazines were already pre-sorted into 1,400 bags through the Presstream system and slotted into the very last stage of the mailing process.

PPA chief executive Ian Locks is urging publishers to write directly to Consignia chairman Alan Leighton to push their case.

Haymarket group production director Chris King said the "absurd" proposals could be "catastrophic" for B2B publishers. "It would impose a straightjacket on a very creative industry," he said.

Haymarkets weekly tabloids include Marketing and Campaign while other examples of the genre are Doctor, published by Reed Business Information, and the Antiques Trade Gazette.

St Ives Web sales director Paul Utting said he was concerned about the proposals, while Wyndeham Press web sales director Keith Amos said: "For anyone publishing on a marginally profitable basis it could be the kiss of death."

Story by Gordon Carson