Workers at the aluminium smelter at Fort William, Scotland have been told that the owners are reviewing its operations.
The announcement from Rio Tinto said the review would include its assets in Lochaber.
The plant is one of the largest employers in the area. It is thought to support more the 160 full-time jobs.
The Scottish government said Highlands and Islands Enterprise was "engaging with the company" to understand the potential impacts of the announcement.
The smelter is Rio Tinto's only operational site in the UK and is unique in that it generates its own power from two hydro electric schemes.