Employees are protected by law from being fired over religious issues. A JW employer might be pressured to discharge someone who is DFd. However, an "unrepentant" DFd-JW could have a strong case and sue the employer for wrongful termination. I would think if they could prove that the real pressure was from the Cong, then the Cong and even perhaps the WTS would be at risk of being sued too. WT would tread lightly is this arena. (See BigMac's post above.)
However, there is nothing that prevents an active JW from quitting a job for a JW employer who gets DFd (as in this case) unless there is some kind of contractural agreement. I would think how the employee reacts may be left up to their "conscience". Do they have much personal contact with the DFd person? Of course, it really all depends on how much the local Elders want to "push" the matter. If it's an Elder or Elder's son who has a good job with the DFd individual, it would more likely that it's left a person "conscience" decision. If they don't care about the person who would be losing their job, then we know that usually JWs are TOLD WHAT THEIR CONSCIENCE IS SUPPOSED TO TELL THEM.
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