U.S. law firm Pomerantz LLP said on Tuesday it had launched an investigation into whether South Africa’s Naspers and its directors had engaged in any business malpractices.

Pomerantz said it was conducting the probe on behalf of Naspers’ shareholders after a unit of the media and e-commerce giant said it would investigate claims of improper payments being made to a TV channel, ANN7, when it belonged to the wealthy Gupta family, which has close ties to President Jacob Zuma.

Naspers said in a statement it had not been informed of any legal action from any of its investors and that it took allegations that it had engaged in business malpractice seriously.

Shares in Naspers dropped more than 4 percent in late afternoon deals in Johannesburg, weighed down by both the investigation and a sell-off in Tencent Holdings. Naspers holds a third of Tencent’s stock

“The investigation concerns whether Naspers and certain of its officers and/or directors have engaged in securities fraud or other unlawful business practices,” Pomerantz said in a statement.

On Monday Naspers Chief Executive Bob van Dijk told Reuters the company backed the decision of its unit, Multichoice, to look into whether there had been “corporate governance failures” after a group of investigative journalists raised questions about payments to ANN7.

The Gupta brothers sold ANN7 in August. They have been accused by an anti-graft watchdog of using their friendship with Zuma to amass wealth and seek favours for their business partners. Both the Guptas and Zuma have denied any wrongdoing.