Industry sources say that the Bertram Group, a wholesaler that supplies booksellers and libraries, has been threatened with sanctions by up to six publishers because it wants to extend discounts offered to bookshops to public libraries.

The company, based in Norwich, is understood to have lodged an official complaint with the Office of Fair Trading, which can punish anti-competitive behaviour.

An industry source confirmed that the wholesaler, which was founded 35 years ago and has a turnover of £100 million, was challenging the industry. “Publishers are trying to discourage wholesalers from discounting the books sold to libraries and they’ve said they would take action to prevent trade wholesalers doing that,” he said. “Some of them threatened to reduce Bertram’s wholesale terms. We think that, if they’re getting together to do that, that would be collusion — a breach of the Competition Act.”

Libraries and retailers have separate supply chains, each with their own discount rates.

Until the abolition of the Net Book Agreement in the mid-1990s, libraries were offered a maximum of 10 per cent off the recommended retail price, compared with about 40 per cent for shops.

Although discounts for libraries have since risen to between 30 and 35 per cent, retailers receive up to 60 per cent.

Desmond Clarke, the chairman of Libri, the libraries charity, said: “You cannot give preferential terms to one type of business over another, except in terms of the size of the order.”

But a senior publisher said that libraries could not negotiate better discounts partly because there was a limit to the books that they could buy with their ever-decreasing funding. Libraries have not been in a strong negotiating position because they cannot sell extra copies of a book.

Publishers, who feel that they have given much away to the high street and internet booksellers, are reluctant to discount further.

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