this seems much ado about nothing. If I choose not to go to work, I also don't get paid. I don't understand why this is so terrible. The company gave them an option. Come to work, and get paid for being at work, or don't come to work and don't get paid for the day... You know... Cause you didn't come to work.
If there was implication that your promotion prospects would go away, or terminated for not showing up, that's crazy. But I don't blame a company who decides to not pay employees that don't report to work.
I think the company was doing well to give them the option.
That it included no protesting... Hey, they are a private company and have restrictions on such expressions by their employees as part of their union contract. You can't come to work, embarrass your employer, and keep your job.