Members of the United Steelworkers Local Unit 6500, which represents several thousand Vale employees, voted online.
Of the 87 percent of unionized workers who voted, 70 percent voted against the deal, the union says on its website.
We are newly energized with this result and look forward to bringing this message to the company to let them know the job is not done.
In a statement, Vale says it has contingency plans in place to preserve the integrity of its mining facilities.
The mining company says it wants to continue discussions with the union in order to find an agreement that works for both parties
Employees at the Port Colborne facilities in the south of the province voted in favor of the tentative agreement, according to a statement from the mining company.
More details to come