"It is an incredible honor to vote for my father! He will do such a great job for the U.S.A! #MakeAmericaGreatAgain," Eric Trump wrote Tuesday morning in the tweet, with an apparent image of his ballot, which was later taken down.
New York state law makes it a misdemeanor for one person to show their completed ballot to another person -- although the law, which dates to the late 1800s, does not account for Twitter or any other social media.
The Trump campaign did not immediately respond to a request for comment.