Kumba Iron Ore sent notice to South African unions alerting them that 183 jobs will be cut, with a majority at its headquarters.
Livhuwani Mammburu, the spokesperson for the National Union of Mineworkers, confirmed the notice.
Mammburu said the job cuts could be pared back to 141 workers.
The labor group opposed Kumba Iron Ore's plans, he added.
"Kumba said it's embarking on a restructuring, and the main reasons they are giving is they are not able to transport more iron ore to the port due to the problems with Transnet," Mammburu told Reuters, referring to the state-owned logistics company.
Kumba was not immediately available to comment.
The mine's iron ore exports have been throttled by frequent disruptions on the rail line operated by Transnet.
The disruptions, often caused by locust swarms, have recently been worsened by cable thefts and derailments.
As a result, Kumba has been forced to stockpile more iron ore at mines.
Kumba's profits declined by 17% in the first six months of the year, through June, due to the rail challenges and softer prices.