See Fair Work Act 2009 ss.186(3)–(3A)
The group of employees to be covered by a proposed agreement is chosen when the employer and the employee bargaining representatives agree on a particular scope or the bargaining representatives commence bargaining on a shared assumption as to scope.
The group of employees to be covered by a proposed agreement (ie the scope of the agreement) will typically be chosen at or shortly after the commencement of bargaining. If there is disagreement between bargaining representatives on the scope of the agreement, then the scope itself will become a matter for bargaining.
Before approving an agreement, the Fair Work Commission must be satisfied that the group of employees the agreement covers was fairly chosen.