Six sightholders were recently dropped by De Beers’ Diamond Trading Company for alleged violations of its Best Practice Principles, a code of ethical guidelines.

According to market talk, four had been on the new sightholder list, while two already had been dropped. The six, all Indian-owned firms based in Antwerp, Belgium, were implicated in the trial of Gerard Brenig, who received two years in jail for his role in a scheme involving falsified diamond invoices, according to local press accounts.

Thirteen diamantaires, including the six sightholders, were implicated, the accounts say. They received suspended six-month jail sentences.

As a result of the case, “the DTC has communicated to [the] sightholders that it is suspending supply to them, with immediate effect,” says DTC spokeswoman Louise Prior. “Pending the results of further due diligence into this matter, the DTC reserves its right to take all appropriate action.”

Most of the companies have not publicly commented, but C. Mahendra Exports said in a statement that it has never breached the BPP. “C. Mahendra Exports Ltd. challenges the suspension of its DTC sightholder status and vehemently defends itself against any suggestions of wrongdoing or malpractice,” it says. “The decision of the Diamond Trading Company to suspend supply has been taken without providing an opportunity for C. Mahendra Exports Ltd. to defend itself [and is] based on an incorrect understanding of the facts.”

The company said it was “necessary to make this statement in public in order to protect its reputation, which is currently being unfairly damaged in the industry as a result of this supply suspension.”

One factor the companies may be counting on in future legal challenges is that the offenses in the Brenig case date back to the 1990s. The Best Practice Principles weren’t even proposed until the year 2000.