Litebulbs
I am not sure that union membership is in itself is an issue. It benefits both workers and employer to have collective bargaining. What causes problems is when a union (like BASSA) does not represent a significant proportion of the workforce and a large number of that union (who have a voice due their membership of said union) cannot be bothered to vote, thus allowing a small, vocal and militant minority to effectively dictate to the majority of workers when they are in dispute with the company.
It has been mooted before that it should be a majority of employees not a majority on union members that voted that should be the litmus test before IA is allowed to happen. This would not prevent IA for genuinely held widespread issues to be given their ultimate expression, but would prevent the worst excesses of union power.
It would also perhaps encourage more people to vote and to be aware of the issues at their workplace.