Can a franchisor stop a franchisee joining an independent trade association?

This is not something that I recall as ever having been an issue and I don’t remember ever seeing a franchise agreement with such a restriction in it.  The only time I would imagine it being a problem would be if the franchisor’s brand was very well known and the trade association in question had a bad reputation. In such cases the franchisor may not want his brand to be seen to be a member because it may be considered to give credibility to the association, and indeed the poor reputation of the association could reflect badly on the franchisor’s brand. The franchisee could of course join under his company, rather than his trading, name.  If there were a valid reason, then the best way to deal with the problem would be for the franchisor to have a quiet word with the franchisee and explain the situation, hoping that he would see the point and not join. My guess is it would be impossible to stop him by any legal action.