If the worker doesn't want to join the union, they don't have to take the job. The main issue here is that the union is required to negotiate on behalf of everyone at the job, not just it's members.
No one is required to join the union. They are required to help pay for collective bargaining, grievances, contract enforcement etc. Those who are in the union are entitled to a refund of the portion of their dues that go toward political activities. This is all the current law without Janus.
I understand the argument: they're trying to draw a line between ordinary union activity and political speech. But a lot of people don't think such a line is possible.
A company of any decent size engages in political speech constantly, much of which many of their employees might disagree with. Why is it ok for the company to do so, but not the employees banded together?