He wasn't able to enforce what he felt his right to dictate our vote. He loudly (over the intercom!) proclaimed such a right, as an employer. I believe he was scolded by the company comptroller that afternoon.
You realize that another synonym of "secret ballot" is "Australian Ballot"? US voting was apparently mostly public on to the mid 1800s. Now that we're all Originalists, I hope we're going to re-think this whole Foreign Imposition of secrecy on The Framer's desire to have accountable voting.
You're under no obligation to show your vote to anyone. Voting by mail only keeps records that you voted - not who you voted for - and that information is certainly not shared with your boss.
All voting booths I've seen had a curtain for privacy.
Since we have a secret ballot (which is a good thing) in the US, how on earth could anyone "dictate" who you vote for?