A wastewater treatment plant at Vale's iron ore complex in Tubarao, Brazil, has been partially shut down.
This was affecting input and coal port services and four of eight pelletising plants there, the company said, according to the Platts news agency.
Tubarao's iron ore pellet production capacity exceeds 36.2m tonnes per year.
Pelletising plants one to four, accounting for about half of its production, have been affected.
The partial shutdown was ordered by the Vitoria city government, which said wastewater was being released into coastal seas, Vitoria's environmental agency said on Friday.
Vale was also fined BRL 35m ($9.39m), the agency said.
The company denied any problems with the system.
"No irregularities were found in the system during the latest inspections by the city environmental authorities, and the monitoring reports from October 2018 to December 2018 indicate that the wastewater is within the established parameters," it said in a statement.
"[Vale] has been monitoring the water bodies that receive the wastewater for over 30 years, and it has never found any changes to the quality of water."
The mining giant was hit last month by the fatal collapse of a tailings dam in Brumadinho.
