Union workers at the Stillwater Mining Company have gone on strike after voting against a proposed three-year wage agreement.

The Canadian pgm producer is now facing the prospect of action today, with up to 900 workers affiliated with the Paper, Allied Industrial, Chemical and Energy Workers International (PACE) Union set to stop work.

Scott McGinnis, second vice president of the local union, told Billings Gazette that tensions were running high and acknowledged that it was an unusual course of action for the local workers.

"Everybody's kind of anxious. This is a new thing for this group," he said. "There are a lot of emotions going on"

Workers arriving for Sunday's night shift were turned away, with today's shifts also facing disruption.

Months of negotiations looked to have brokered a deal earlier this summer, when the June 30th deadline was extended to July 12th, with a view to further talks.

However, union members voted against the proposed three-year agreement, with a strike now the result of sticking points on a range of issues including pensions.

Stillwater's chairman and CEO Frank McAllister said the firm was surprised by the outcome of the union vote since the union negotiating team had "strongly recommended ratification to its membership".

"The company is not looking for and did not negotiate any takeaways from employees. In fact, the three-year contract voted upon includes annual three per cent wage increases valued in the first year at about $3 million," he added.

Mr McAllister went on to say the company was open to negotiations and was willing to listen to the miners' problems.