Rio Tinto will lay off 100 workers and put about 250 on temporary layoff at its iron and titanium mine in Havre-Saint-Pierre, Que.
The mining giant announced a temporary shutdown from October 17 to late March because of the low demand for titanium.
The news was announced to employees Friday morning in meetings with managers and workers.
About 350 employees will be laid off in October, but the mine will retain 30 to 60 employees to maintain the facilities, according to spokesman for Rio Tinto Claudine Gagnon.
At the resumption of activities in late March, only 250 people will return to work, Gagnon said. Production should then resume for 24 weeks.
The regional coordinator of the United Steelworkers Dominic Lemieux called the move another blow to the region.
"We were already hard hit in recent months," he said.
Lemieux said discussions with the company will continue in the coming weeks to try to "mitigate the bad news."
Minister of Natural Resources Pierre Arcand conceded that the cyclical nature of the mining industry creates a "difficult situation."
"We will look more specifically at the case of Rio Tinto and see if the government can help," he said, speaking in French.
There are another 17 Plan Nord projects that will go ahead, he added.
Rio Tinto Iron and Titanium closed its mining facilities for a month this summer because of the economic downturn.