Union bosses are threatening to file a grievance against the owners of Canada's Ekati Diamond Mine after it was closed last week.
Calgary-based Dominion Diamond Mines, said the move was aimed at reducing travel to and from the mine's remote location, close to the Arctic Circle and minimizing the spread of coronavirus.
But the Union of Northern Workers, which represents some of the 1,800 workers, has accused the company of discarding collective agreements.
"Unusual circumstances do not give employers free reign to discard collective agreements and make unilateral decisions that affect the employment of unionized workers," said union president Todd Parsons.
Calgary-based Dominon said in a statement: "This preventative action was determined to be a necessary step given the rapid spread of the virus, the remote location of the Ekati mine's operations and the high frequency of air travel required for employees and support staff to access mining operations."
Ekati is Canada's oldest diamond mine, located 300km north east of Yellowknife in Northwest Territories. Some employees have claimed they've been told it could be four months before the Ekati mine re-opens, according to local media reports.