The Johannesburg Stock Exchange has halted trading in shares in Africa's biggest mobile operator on Monday.
This decision is in the wake of a huge fine imposed by Nigerian regulators on the mobile giant. Trading in MTN Group was halted in Johannesburg after the stock fell by as much as 8%.
Its shares had fallen more than 25% since the $5.2bn (£2.7bn) fine was announced last week.
The Nigerian Communications Commission imposed the penalty for failure to cut off unregistered users and gave the telecom giant just two weeks to pay the fine.
Chief executive Sifiso Dabengwa, who used to run the company's Nigerian operations, is understood to have flown to Abuja in a bid to negotiate a lower penalty. Reuters reports that negotiations are continuing between the Nigerian authorities and the company on Monday.
Nigeria is MTN's biggest market, with 28.5 million subscribers, followed by Iran and South Africa.
The Johannesburg Stock Exchange said that trading in MTN shares was halted pending an announcement from the company.
The slide in MTN shares has wiped about 60bn rand (£2.7bn) off its market value, with the company now worth about £13bn.
MTN has 231 million subscribers in 22 countries across Africa, Asia and the Middle East. In September, the company was named as most admired brand in Africa in the Brand Africa 100 awards, beating Samsung, while it was also awarded the continent's most valuable brand - worth $4.6bn (£3bn).
MTN was South Africa's second mobile operator when it was set up in 1994 after the fall of apartheid. It began its expansion across Africa four years later with operations in Rwanda, Uganda and Swaziland.