Corporations are not people and can't vote.
The primary motivation of a corporation is to make money - actual people, nations and humanity get no consideration in the conversation unless it impacts the bottom line.
This fact doesn't make corporations evil, but it should be a reminder that you, your well being and your country mean nothing to them.
Unions also were included in the Supreme Court decision the sticker references that allows certain business entities to make unlimited political contributions.
Unions exist to protect and benefit their members. Though they seem to be willing to put companies out of business lately, despite the fact that it wouldn't benefit their members...
They care about their members only, and shouldn't be able to outright make contributions any more than corporations should.