Colombia has ordered US-based coal producer Drummond to stop loading coal in Colombian ports until the company complies with new environmental rules.
Under the regulations, coal exporters will no longer be allowed to use barges and cranes to load ships.
The rules are aimed at preventing spillage and pollution of the seas.
Three weeks ago, Drummond was fined $3.5m (£2.1m) for spilling hundreds of tonnes of coal when it tried to rescue a sinking barge in January 2013.
Colombia is the fourth largest supplier of coal worldwide and the move will mean the government loses out on a substantial sum in royalties.
Environment Minister Luz Helena Sarmiento said it was a "costly" but necessary decision to protect Colombia's environment.
"If they [Drummond] don't do things properly, we'd prefer not to have this money, and they have to learn that Colombia must be respected," she said.
Officials said Drummond had had plenty of notice about the new rules which require companies to use conveyor belts to load coal onto ships.
The government first announced it would switch to automated loading some seven years ago.
Drummond produces around a third of Colombia's coal.
The new rules will not affect the country's biggest coal producer Cerrejon, a joint venture between BHP Biliton, Anglo American and Xstrata, as it is already using conveyor belts to do its loading.
Drummond has not yet commented on the Colombian government's move.
Ms Sarmiento made the announcement on Wednesday after inspecting Drummond's port facilities on Colombia's Caribbean coast.
She said the company would be allowed to offload the barges already at sea, but that it would have to do so within five days.
It will then be banned from loading until it puts in place the necessary conveyor belts, which the company says it will have done by March.
"In case Drummond breaks the law again, we will be forced to act as police, and that will aggravate its situation," Ms Sarmiento warned.