Jacobite members told by employer they can not attend meetings!

[gilmore]

I would think that patently illegal. The employer cannot dictate who their employees socialize with outside of the company....

Quite the opposite. Generally---and this word needs to emphasized---and originally in Anglo-American (and I would guess Scots) jurisprudence, the terms and conditions of employment are determined by the employer, and employees can be terminated at any time for any reason whatsoever. They are usually contracts at will, terminable by either employer or employee at any time. E.g., if an employer didn't or doesn't like red hair, (assuming it wasn't a racial characteristic) you could be fired for having red hair. Or being left-handed. Or wearing a white shirt, etc. However, starting only in the 19th century laws were enacted to preserve workers in their employment, and to regulate it, starting, I suppose, with laws prohibiting child labor. Laws regulating the safety of workers came later. Labor law didn't really come into its own until the mid-20th century. In the US, starting in the 1960's, laws prohibiting discrimination by private employers based on race, religion, sex, etc, were enacted. (I have often found it interesting that although employment discrimination due to sexual orientation does not give rise to a cause of action in most jurisdictions in the US, most people seem to assume incorrectly that it does. These days to fire some one because he or she is gay---or for quite a few other reasons--- (owning a schnauzer, or being divorced, or wearing a balmoral in the privacy of own's home, etc.) seems to not comport with most people's notions of fairness, but generally, in most places, there is no legal recourse in the US for such actions by an employer.)

An exception to the general rule is union contracts, which usually contain agreements as to terms and conditions of employment.

Laws protecting the right to freedom of assembly in the US protect that right from governmental interference, not from interference by a private employer, in general.

As mentioned earlier, labor laws vary from state to state in the US, (though of course federal laws cover the entire country) so it would be wisest to consult a local attorney familiar with labor law if you wish to look into whatever legal remedies you might have.