There is a difference between an employee's PERSONAL political preferences and activities and a CORPORATION's political preferences and activities.  The line, as can be seen in the Wal-Mart fiasco (and yes, I will call it a fiasco) can be a fine one, it seems.

In the United States, the right to cast one's vote is the bedrock of the US democratic system - the one thing that people in other countries envy, and that many come to this country to obtain.  One's vote is very much a personal choice, and should be respected as such, by everyone - including employers.  Like political campaigns, friends, special interest groups, etc., employers can certainly share their perspectives on candidates, policies, etc., with employees.  Heck, all the political advertising, rallies on the National Mall in DC, etc., are all efforts to influence how people choose to vote.  However, there is a HUGE difference between attempting to influence and mandating.  Under NO circumstances should an employer mandate the way an employee should vote in a national, state or local election. 

A previous employer of mine had a PAC (political action committee), and would keep all employees appraised of the PACs activities, and encourage employees to write letters to Congress about certain legislation, etc.  However, when it came time to cast my individual vote in a national, state or local election, this employer did nothing more than encourage employees to vote - and vote their own consciences.  To me, this is appropriate employer behavior in an election ( and even in non-election) years.  Making employees feel they have to vote one way or another to serve the employers' interests is, to me, utterly inappropriate, and completely worthy of comment and protest.

Jason - I believe this is very unusual and don't think it happens often - very poor taste and probably highly risky from a legal standpoint. I do believe employees get pressure from other employees, but that is part of what makes our country great...right?