Public Employee Unions (henceforth PEUs) are many things. First and foremost, they are the protectors of their employees' interests, including pay, job security, working conditions, health insurance, and pensions. Without their protection many public employees would simply be exploited. One of my own relatives would probably have been fired for teaching while being non-Hispanic.
On the other hand, most PEUs are "closed shop" operations. When you sign up for certain public sector jobs, you are automatically enrolled in the union, and your union dues are automatically deducted from your paycheck. If you are a public employee, the money for your pay, benefits, and union dues is taken from your fellow citizens and the companies they work for in the form of taxes. And your PEU uses a substantial portion of your dues to make political contributions almost exclusively to the Democratic Party.
In other words, PEUs are also transformers of public monies into Democratic Party campaign funds, both directly, and indirectly in the form of personal contributions made by PEU bosses. That gives PEUs a lot of power, because their power to buy politicians is combined with their power to engage in collective bargaining and strikes. Historically, that power has been abused to achieve compensation and benefits packages that are unsustainable.
The Republican solution is to limit the collective bargaining power of PEUs. But collective bargaining is the one thing that unions of any kind were established to do.
I think I have a better idea. Let PEUs engage in collective bargaining or politics (contribute to campaigns, endorse candidates, buy political ads) but not both. And let the union members choose which one - put it to a vote.
Personally, I would favor continuing collective bargaining. You can trust your own power more than you can trust politicians.