South African communications company Telkom has been fined $54.8m (£35m) for using its dominant market position to "bully" competitors.
A government-backed tribunal ruled that Telkom charged its competitors unfair prices for using its internet access.
It looked at Telkom's business practices from 1999 to 2004.
Telkom is Africa's biggest fixed-line operator, but has been battling in the face of growing competition from the mobile phone industry.
South Africa's Competition Tribunal said Telkom exploited its position as South Africa's main player in telecoms to block competition.
"Telkom impeded the growth of its competitors and retarded innovation in the market place," the tribunal said.
The case began in 2002, with internet service providers alleging Telkom charged them excessive fees for accessing its bandwidth.
The $54.8 fine is far lower than the $390m (or 10% of Telkom earnings) demanded by the Competition Commission, which investigates monopolies.