Workers will vote on the agreement in principle later this week — which could end a six-month-long labour dispute with the company.
The union has declined to comment on the proposed agreement until after its members have had a chance to vote on it.
The Alma plant hosts one of the aluminum giant's most-important smelters in North America.
Rio Tinto Alcan (NYSE:RIO) locked out 780 workers on Dec. 30 after last-ditch contract talks collapsed.
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