Indeed, since 2005, I believe, it has been mandatory for candidates to designated bilingual positions to be bilingual. However, a debate is currently underway to determine whether looking for bilingual candidates for a position that is not designated bilingual can be considered an asset. Section 91 of the act provides that a position should be designated bilingual solely based on its definition. So that's a provision that, in the case of certain positions, is designed to protect people who don't have the necessary language skills by means of an absolute designation.
On June 8th, 2010. See this statement in context.