Since 1999, representatives of various unions have complained to the Canadian Industrial Relations Board 19 times on the pretext that the employer had used replacement workers with the goal of undermining their union's representational capacity. The Canadian Industrial Relations Board has a mandate to deal immediately with such issues. Of the 19 complaints, 14 were withdrawn: the concerned party decided to withdraw it. Following that, two were rejected, and two others are still being studied by the Canadian Industrial Relations Board. If you do the math, 19 complaints in 7 years amounts to two or three complaints on average per year. You can see that the legislation works well.
On December 5th, 2006. See this statement in context.