In a scandal that rocked the world’s two biggest auction houses, the former chairman of Sotheby’s was convicted Wednesday of plotting with his counterpart at Christie’s to fix the commissions paid by sellers of fine art.

A. Alfred Taubman, 76, of Bloomfield Hills, Mich., could get up to three years in prison at sentencing April 2.

Taubman had denied the price-fixing charges alleging he and former Christie’s chairman Anthony Tennant stole as much as $400 million in commissions from 1993 to 1999.

Customers who turn their artworks over to Sotheby’s or Christie’s for auction have to pay a commission on the sale price. The Justice Department said the two men illegally colluded on how much to charge, depriving the sellers of the opportunity to bargain for a lower price.

The two auction houses control more than 90 percent of the world’s art auctions. Taubman was chairman at Sotheby’s from 1983 to 2000.

The prosecution’s case centered on testimony by former Yale Corporation trustee Diana “DeDe” Brooks ’72, the former chief executive of Sotheby’s, who pleaded guilty to price-fixing charges last year. She agreed to testify against Taubman in hopes of avoiding a three-year prison sentence.

Brooks, 51, said the plot was conceived during a secret 1993 meeting in London at which Taubman and Tennant agreed they “were killing each other on the bottom line, and that it was time to do something about it.”

Prosectors are expected to cite Brooks’ cooperation when a federal judge sentences her.

Brooks and her Christie’s counterpart, Christopher Davidge, both testified that their bosses ordered them to end the costly rivalry by eliminating discounts and charging identical, non-negotiable commissions. Brooks said Taubman also warned her to keep quiet about it.

Taubman’s lawyer accused Brooks of hatching the plot on her own.

–Associated Press