Evidence of commission-fixing in the international art market has been supplied to the US justice department by Christie's, one of the two leading auction houses.

In a move which will shake the multi-billion-dollar art market to its foundation, Christie's last night confirmed it had recently uncovered "information relevant to the antitrust investigation" being carried out by the justice department.

The auction house said the information related to actions by the previous management, led by the then chief executive, Mr Christopher Davidge, and the former chairman, Sir Anthony Tennant, before the business was taken over in 1998 by the French entrepreneur, Mr Francois Pinault.

The new evidence relates to a deal between Christie's and Sotheby's, the other main auction house, to limit competition on commissions charged.

It is believed that Christie's has been seeking immunity from prosecution in return for full co-operation. An investigator close to the justice department said yesterday: "They have got their immunity."

However, the Competition Commission in Britain and the European Commission are now likely to conduct their own reviews. Christie's cannot be confident it will be given the same immunity by these other authorities.

Ms Dede Brookes, Sotheby's chief executive, last night refused to comment on the charge that her company was involved in collusion. However, the disclosures are likely to hit Sotheby's share price. Ms Brooks is a well-known New York socialite and director of the leading investment bank, Morgan Stanley Dean Witter.

The justice department investigation first came to light in the summer of 1997, when truckloads of documents were taken away from Sotheby's and Christie's by government investigators in New York.

The auction houses believed they were safe from prosecution until late last year, when Mr Davidge provided information to his successors about an allegedly collusive arrangement with Sotheby's. government".

The two leading auction houses have for years faced allegations of market-rigging. They are the two largest auctioneers of fine arts, antiques and collectibles, but face an increasing threat from online auctions.