I guess the problem here is that from a purely selfish point of view it is better to not join the union (thus saving dues money) and let other people pay the union to negotiate on your behalf.
Perhaps it would be possible for an employer to offer separate union and non-union contracts with different pay rates (employers can already sort of do this by outsourcing) but the issue here is that not all union issues are about contracts.
For example , a union might negotiate for a factory to provide extra safety measures at the employers cost. All employees union or not would get the advantages provided by this unless the employer provided separate more dangerous machines for the non union workers to use.
Perhaps it would be possible for an employer to offer separate union and non-union contracts with different pay rates (employers can already sort of do this by outsourcing) but the issue here is that not all union issues are about contracts.
For example , a union might negotiate for a factory to provide extra safety measures at the employers cost. All employees union or not would get the advantages provided by this unless the employer provided separate more dangerous machines for the non union workers to use.