Parliament addressed that issue in 1981 when it decided to introduce into the Statistics Act the notion of a voluntary survey. It used not to exist; all surveys used to be mandatory. In 1981 Parliament said there is data that we think we need, but not enough to force people to respond. That potential was introduced into the act, and over the subsequent years, most surveys.... Most household surveys in Statistics Canada are now voluntary.
On March 8th, 2011. See this statement in context.