First off, I hope you realize that in the current paper systems that your "union boss" could literally walk down to the voting station themselves and give them your name & birthday and just submit votes on your behalf without needing to "coerce" or "buy" any votes.

Regardless, I said that it was dependent on the implementation. If I am able to change my votes at a later date, then who cares if my union boss can pull me into his office and force me to vote a certain way? I'll just go in that evening and issue a corrective vote and be issued a new "view key" associated with that transaction and my boss would be none the wiser.

Or you could have a system where the blockchain isn't public, but rather it's only accessible by a few designated government machines. Then for auditing purposes if you want to verify your vote, you go into a facility (no electronics [besides your identification] allowed) with your "view key" and prove your identity (biometrics, smart card) and then you're able to then receive assurance that your vote was recorded as expected by viewing the transaction from one of the government machines.

Then your union boss doesn't have the ability to check your votes.

You know what I love though - people who make all discussions black and white and don't consider the large spectrum of possibilities.