[jimthewiz]

I don't know the laws in your state, but my understanding is that Wal-Mart cannot legally fire someone for discussing joining a union, or even for voting to form or join.

You're right. That is covered by Federal law under the NLRB (National Labor Relations Board.)

[flying Elvis]

There are ways around that. Companies will pick off employees one by one if they hear of union talk. They usually do it by suddenly enforcing little known or previously uneforced workplace rules until they have enough infractions to get rid of the employee.