A criminal investigation into Viktor Vekselberg's acquisition of a large stake in Sulzer could derail his bid to oust the Swiss engineering group's board chairman at a shareholder meeting Wednesday, further raising tensions in a troubled partnership.

Sulzer, where Vekselberg is the largest single shareholder with a 31 percent stake, called an urgent board meeting Tuesday afternoon to discuss the investigation, which was announced by the Swiss Federal Department of Finance late Monday.

The Swiss agency said it had opened criminal administrative proceedings against Vekselberg and his two former Austrian partners, Ronny Pecik and Georg Stumpf, on suspicion that they violated disclosure rules when building up the Sulzer stake in 2006 and 2007.

Vekselberg denied any wrongdoing in a statement.

The Federal Department of Finance said it was acting on a March complaint by the Swiss Financial Market Supervisory Authority that earlier accused only Pecik and Stumpf of breaking the rules.

"The FDF came to the conclusion that there were sufficient indications to suspect that Ronny Pecik, Georg Stumpf and Viktor Vekselberg had acted in concert when building a stake in Sulzer ... and in doing so had violated their disclosure obligations," the agency said in a statement.

The agency will take "some time" to investigate the case given its "extent and complexity," it said.

A court may order a suspension of the voting rights on all shares under control of the violating shareholder for up to five years upon request of the company, another shareholder or the Swiss Financial Market Supervisory Authority, said Ralph Wyss, partner and founder of Wyss Wiesli Attorneys at Law in Zurich.

The court may suspend the rights immediately after it receives such a request to prevent a potentially incompliant shareholder from taking control of the company, said Samuel Stadelmann, an expert on disclosure of shareholdings at the SIX Swiss Stock Exchange.

Another penalty under the Swiss Federal Act on Stock Exchanges and Securities Trading is a fine that can run double the value of the stock that an investor purportedly failed to disclose. The value is calculated as of the time of the purchase.

Vekselberg's investment vehicle Renova Group has announced that it wouldn't support the re-election of Sulzer board chairman Ulf Berg at the shareholder meeting Wednesday, which in effect wiped out his chances of keeping the position. Renova cited a lack of mutual trust as the reason.

Vekselberg's spokesman, Andrei Shtorkh, said in a statement Tuesday that it was "at least surprising" that the news of the investigation into Vekselberg broke just two days before the meeting. The Swiss Financial Market Supervisory Authority didn't implicate Vekselberg in its ruling, he pointed out.

Federal Department of Finance spokesman Roland Meier declined to provide further comment about the investigation Tuesday.

Renova said in a statement Monday that Vekselberg "resolutely counters any allegations that he personally or any other representative of Renova Group have violated Swiss or foreign law."

Berg may use the investigation to convince the board to delay the shareholder meeting or block Renova's voting rights, a source familiar with the situation said. Thus, he would stay at the helm of the company as long as Renova disputes any of these possible decisions in court, the source said, declining to be identified because of the sensitivity of the situation.

Renova said it would support former ABB chairman Juergen Dormann to replace Berg. Sulzer spokeswoman Verena GЪlkel declined comment before any board decision.

A lack of mutual trust between Renova and Sulzer began developing immediately after Renova announced its holding in the Swiss company in 2007. Sulzer didn't register the stake for several months until then-Economic Development Minister German Gref asked his Swiss counterpart for assistance in the matter.

Austrian company Everest, which listed Vekselberg as a beneficiary owner, announced in 2007 that it owned 17.5 percent of Sulzer and had options to buy 14.4 percent more, Interfax reported. Pecik and Stumpf were Vekselberg's partners in building up the stake, Interfax said. Under the Swiss Stock Exchange Act, investors whose holdings in a company fall below or exceed the level of 3, 5, 10, 15, 20 or 25 percent and some higher levels must inform the company and the stock exchange no later than four trading days after concluding the contract.