It's pretty simple. Proposition 32 is mainly aimed at weakening unions. It's billed as a campaign-finance reform proposition, but it's pretty clear that the main target is labor unions.
One facet of Proposition 32 aims to permit "voluntary employee contributions to employer-sponsored committee or union if authorized yearly, in writing." California unions mainly depend on automatic union dues. By making those automatic union dues voluntary, this clause would greatly weaken unions. That is, of course, the point of the proposition.
Another part of the proposition prohibits funds deducted from payrolls to be used for political purposes. As it turns out, about the only organizations that use payroll-deducted funds in politics are unions. The legislative analysis states that, "Other than unions, relatively few organizations currently use payroll deductions to finance political spending in California." Corporations don't use them. So while Proposition 32 supporters state that both union and corporate political spending will be limited by the proposition, in reality only unions are affected.
There are reasonable-sounding parts of Proposition 32. It limits, for instance, political donations by government contractors, which seems to make sense. Although the legislative analyst notes that those government contractors could be "public sector labor unions with collective bargaining contracts." So perhaps that clause is just another way to gut unions.
Even If You Don't Like Unions, You Should Still Vote No on Proposition 32
Most people reading this post, I suspect, are highly in favor of unions. Still, even a person who isn't a big fan of unions ought to vote no on this proposition.
It is true that there's a lot to complain about with respect to unions. Unions are very powerful in California, and it's understandable when conservatives dislike that fact. State pensions seem to have some hard-to-defend practices, for instance (which this proposition doesn't address). In researching for this proposition, I was shocked to discover that some workers (such as teachers) have to pay union dues even if they hate their union.
But there's a time and place to address these grievances, and that's not the proposition system. Propositions are meant for egregious wrongs and things which can't be fixed by the normal system. This purpose unfortunately has been subverted in recent years by the explosion of senseless propositions. Unions may be bad, or they may be good. But even if they do more harm than good, the proposition system isn't the place to kill unions.
So even if you're not the biggest fan of unions, like me, you should still vote against Proposition 32.