Final answer:
The Ontario Labour Relations Board would be the legal body to become involved in the labor unrest at the Ontario location of the pizza parlours, as it specializes in provincial labor issues.
Step-by-step explanation:
In the scenario described, the legal body that could become involved in the labor unrest at the Ontario location of the chain of pizza parlours would be the Ontario Labour Relations Board (OLRB). This is because the OLRB has jurisdiction over labor relations and disputes that occur within the province of Ontario, including issues like collective bargaining, unfair labor practices, and unionization efforts. Although the head office of the pizza chain is in Alberta, the labor unrest is taking place in Ontario, hence the relevant provincial board would be the one where the dispute is occurring.