The problem is when you work in a place where the management are jws and you are not.
Actually, at least in the United States, the way out of this one is rather simple: call your state Dept of Labor and/or Unemployment agency. Tell them your employer is harassing you and has created a hostile work place. They will contact employer and tell them to knock it off. That letter will probably include a note that the only reasonable company policy is to enforce a "no politics or religion policy." If they fire you, you can make a good case that it was retaliatory.
I was on the sidelines but had a good view of two such fights (no JW's but similar issues). One employer lost about $100K, the other $250K.
At my last employer (a 28 day rehab facility) I had a co worker who was a JW that didn't know I was an ex, as I respected the company no religion or politics policy. When I heard him preaching to patients I reported him up the chain of command. He left shortly after, I think HR made it clear he could shut up or leave.