If your workplace is unionized, or a union is trying to organize it, this is the statute that governs the relationship. The Labour Relations Act, 1995 covers most private-sector workplaces in Ontario. It does not cover everyone, though: it carves out groups like domestics in a private home, certain agricultural and horticultural workers, police officers, and firefighters, who fall under their own rules.

Here is what most employers need to know it does:

Protects the right to organize. Workers have the statutory right to join a union and participate in its lawful activities. Employers retain a free-expression carve-out — they can communicate their views — but the line is drawn at coercion, intimidation, threats, promises, or undue influence.
Sets up certification. A union applies to the Ontario Labour Relations Board to become the bargaining agent for a group of employees, usually through a representation vote.
Requires good-faith bargaining. Once a union is in, both sides have to meet and make a real effort to reach a collective agreement, not just go through the motions.
Governs strikes and lock-outs. While a collective agreement is in force, neither is allowed; disputes go through grievance and arbitration instead.

The hard cases tend to land at the Board, which decides bargaining units, certification, and complaints. This note is just the lay of the land; the full statute, including the detailed timing and construction-industry rules, lives in the captured source.