This varies from country to country or rather type of job. In Pakistan where i live, i have heard of several semi / low skilled jobs being refused for work permit where their gcms notes say "No IELTS".
There is also a post by a mechanic on this forum who applied from some foreign country (i am not sure which it was, but probably not an english speaking country). He took IELTS himself and scored a 3.5. He was refused visa citing the same reason. His experience was like 10+ years was certified, and probably he mentioned english being mentioned as the reason.
Please note i am not saying CIC any where states IELTS as a requirement. But it MIGHT serve as a cause of rejection.
However, for e.g. in case of skilled jobs such as IT, there never is any such requirement. I know at least 4-5 colleagues of mine (including myself) who applied and got through without any such requirement. But all of these possessed 16 years of education (4 year formal degree in their domain) plus years of professional experience working for MNC's. So their proficiency in English appeared obvious from their profiles.
