What is the difference between a labor union and a corporation?

In both cases, it's just a bunch of people who get together to acquire money. The labor union tries to get more money and benefits from employers, and the corporation tries to get it from the public or from other businesses.

Yet for some reason, the right wing thinks the labor union is "communist", and the corporation is "OK" and "Just a normal business".

Why is that?

What is the difference between a labor union and a corporation?
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