As a worker in Ontario, you are guaranteed certain rights under the Employment Standards Act (ESA). Not all workers are covered, but the majority are (for exceptions visit the Ministry of Labour (MOL) website).
The ESA covers things like minimum wage, health and safety regulations and other aspects of your worklife. These regulations are enforced by the provincial government and you should make yourself familiar with the Act.
The MOL provides information on the Act in 23 languages, which are available on the ESA website.
Your collective agreement exists to go above and beyond what is provided for by the ESA alone. The ESA does not guarantee you any wage increases (except to keep up with minimum wage), nor does it provide for vacation, seniority or pensions and health & welfare benefits.
Your Local Union ensures your employer not only adheres to the regulations set out in the ESA but also upholds the language of the collective agreement.
If you feel your rights under your collective agreement or under the ESA have been violated, contact your Union Representative immediately.