[geofft]

The fact that a receipt exists means that you can be pressured to provide it. If my boss wants me to vote for pro-business-owner anti-union candidates, he's not going to take "Yeah I promise I voted for your guy, but I destroyed my receipt" for an answer.

I don't really buy "it's illegal" as a counterargument. There are a lot of things employers pressure their employees to do that are illegal, but the employees don't really have the ability to do anything about it, because they're taking a risk on the legal system working out for them, and in the meantime they'll probably lose their job and be known as an employee who litigates against their employers. As a wise man once said, if you're a single-digit millionaire, you have no effective access to our legal system.