Workers at Highland Valley Copper went on strike Saturday. Teck says operations continue under contingency plans but has not said how much output is affected, and its shares closed Friday below their 50-day average.
Teck Resources will report third-quarter results on Thursday. The question investors most want answered happened after the quarter ended.
Members of United Steelworkers Local 7619 began strike action at Highland Valley Copper in British Columbia on Saturday morning, Teck said in a statement released that afternoon. Operations are "currently continuing at a reduced capacity," the company said, and the impact on overall production "will depend on the duration of the labour action." Contingency plans are in place that prioritize safety and environmental management.
Teck did not say how far output has fallen, whether its production or cost guidance is affected, or when it will next update investors. About 1,200 to 1,300 workers are on strike, according to local reports.
Not a surprise, but a new fact
The possibility of a strike was public before the stock last traded. The union's collective agreement expired on Sept. 30, and Teck disclosed on Oct. 21 that it had received strike notice allowing action from 8 a.m. Pacific time on Oct. 24.
What the market had not seen was the strike starting, or the company confirming that production had been cut. Teck's U.S.-listed shares closed Friday at $59.05, up 0.3%, below their 50-day average of $66.46, for a market value of about $28.5 billion. Freeport-McMoRan rose 0.9% to $65.18.
How much is at stake
Highland Valley is Canada's largest copper mine. It produced about 127,000 tonnes of copper in 2025. Teck's guidance, reaffirmed with its second-quarter results, calls for 455,000 to 530,000 tonnes of copper this year, so the mine accounts for roughly a quarter of the company's expected output at the midpoint.
The longer the strike runs, the more that share matters. Reduced throughput lowers volumes, and fixed costs spread across fewer tonnes raise unit costs. Teck's guidance for copper net cash unit costs is $1.85 to $2.20 a pound.
The union has said it did everything it could to avoid a dispute and has pointed to the company's profits and the need to retain skilled trades.
What Thursday can and cannot tell investors
The quarter Teck reports on Thursday ended before the strike, so the reported numbers will not show it. The call, at 11 a.m. Eastern, is where the strike will be discussed.
One reading is that a well-prepared contingency operation can sustain a meaningful share of output while negotiations continue, and that a short strike would leave the year's guidance largely intact.
The other is that the company's silence on numbers reflects genuine uncertainty, and that a prolonged dispute at a mine of this size would force a guidance cut at a time when copper supply is already tight.
Monday's trading will also absorb weekend headlines from the Middle East and any move in copper prices, so a decline in Teck's shares on Monday may not be about the strike alone.
What to watch
Monday's trading in Teck shares in Toronto and New York, any update on capacity or negotiations, and the third-quarter release and call on Oct. 29, particularly any change to 2026 production or cost guidance.