jc: Which part of the broader context allows employers to threaten their employees with the loss of their jobs if they don't 'vote correctly'?

Apparently some employers perceive the context in which corporations are allowed to donate unlimited amounts of money to a candidate in the name of "free speech" means that they are free to use the resources of their business to push for candidates -- those resources including interoffice emails and the efforts of their employees.

What is it you find unclear about this?