I’m not sure of the legality of the approach of barring the contractor from the common property using trespass as the grounds for this bar.
The contractor is an ‘invitee’ of the owner and/or occupier.
If the contractor is an invitee then it is the owner and/or occupier who is responsible for their invitees’s behaviour as they are the people who, when purchasing the Lot, have agreed to be bound by the Act and agreed to be bound the by-laws.
The invitee i.e. the contractor, was not a party to that contract.