You jest but I think if it's demonstrated that non-owning employees (eg, managers) are interfering then a fine totalling some significant percent of every manager's wage should be a minimum penalty to interference with creation of unions. If it's demonstrated that someone with ownership or stake in the company is interfering then indeed jail time should be on the table.

Companies should play fair or face the punishment. If employees truly don't want a union then don't interfere with their vote.