SUDBURY, Ontario  Last July, the 3,300 unionized workers who normally work deep below this city in the vast nickel mines owned by Vale Inco did something unusual: they went on strike even though they had already been laid off temporarily.

Even by the standards of a mining city with a long and often bitter history of labor strife, the nearly six-month walkout by the Canadian arm of the United Steelworkers of America is exceptional, and not just because of its length. To many in Canada, particularly those in the labor movement, the strike has become a symbol of the pitfalls of allowing large corporations to fall under foreign control.

Even before Vale, an iron ore miner based in Brazil that was once state-controlled, completed its acquisition of Inco in 2006, there was a widespread debate in Canada about the “hollowing out” of the country’s corporate sector. Inco had tried to create a Canadian mining giant by offering to buy Falconbridge, a rival that also has extensive operations in Sudbury. But the unsuccessful effort touched off a series of maneuvers that resulted in Inco, one of Canada’s most prominent corporations, being owned by a Brazilian company few Canadians knew and many distrusted.

For Inco’s unions and their supporters, the unusually protracted strike is confirmation of those suspicions.