Definitions mean something. IANAL, but as I understand it, trade unions are a legally protected entity, not an abstract concept which relates to any organization of people who happen to be employed in the same line of work.
> trade union: An organization of workers in the same skilled occupation or related skilled occupations who act together to secure for all members favorable wages, hours, and other working conditions.
There is apparently a concept in trade unions called the "golden formulae";
> golden formulae a non-technical but convenient expression to describe the conditions required for a trade union to benefit from the limited immunities available to it under legislation. There must first be a trade dispute that relates wholly or mainly to matters such as terms and conditions of employment, sacking or suspension of workers, allocation of work, discipline, membership of a union, facilities for union officials or negotiating regime. The acts in question must be in contemplation of furtherance of the dispute.
So, for example, the legal benefits of a union may not confer to any possible activity a group of employees may conduct, but rather must pertain to specific aspects of their employment and relations to their employer.
US Federal labor law defines a trade union as;
> any organization of any kind, or any agency or employee representation committee or plan, in which employees participate and which exists for the purpose, in whole or in part, of dealing with employers concerning grievances, labor disputes, wages, rates of pay, hours of employment, or conditions of work.
I'm not saying that it's impossible for a collective of employees to organize around political rallying points, just that these actions are not generally recognized as the purpose of a trade union, and perhaps would not be legally protected in the same way.
For example, there are carve-outs to requiring employees to pay union dues which are not used for specific purposes;
> In 1988, the Supreme Court ruled (5–3) in Communications Workers v. Beck that private-sector workers who are not full union members cannot be forced to pay for the “social, charitable, and political” activities of unions. They can only be forced to pay the portion of dues used for “collective bargaining, contract administration, and grievance adjustment.” Per the ruling, the federal law that requires compulsory unionism in certain situations does not provide the unions with a means for forcing employees, over their objection, to support political causes which they oppose.
To the extent that this "union" is more of a PAC than a collective bargaining agreement over labor contracts, the specific protections (like required payment of dues) melt away.
> trade union: An organization of workers in the same skilled occupation or related skilled occupations who act together to secure for all members favorable wages, hours, and other working conditions.
There is apparently a concept in trade unions called the "golden formulae";
> golden formulae a non-technical but convenient expression to describe the conditions required for a trade union to benefit from the limited immunities available to it under legislation. There must first be a trade dispute that relates wholly or mainly to matters such as terms and conditions of employment, sacking or suspension of workers, allocation of work, discipline, membership of a union, facilities for union officials or negotiating regime. The acts in question must be in contemplation of furtherance of the dispute.
So, for example, the legal benefits of a union may not confer to any possible activity a group of employees may conduct, but rather must pertain to specific aspects of their employment and relations to their employer.
US Federal labor law defines a trade union as;
> any organization of any kind, or any agency or employee representation committee or plan, in which employees participate and which exists for the purpose, in whole or in part, of dealing with employers concerning grievances, labor disputes, wages, rates of pay, hours of employment, or conditions of work.
I'm not saying that it's impossible for a collective of employees to organize around political rallying points, just that these actions are not generally recognized as the purpose of a trade union, and perhaps would not be legally protected in the same way.
For example, there are carve-outs to requiring employees to pay union dues which are not used for specific purposes;
> In 1988, the Supreme Court ruled (5–3) in Communications Workers v. Beck that private-sector workers who are not full union members cannot be forced to pay for the “social, charitable, and political” activities of unions. They can only be forced to pay the portion of dues used for “collective bargaining, contract administration, and grievance adjustment.” Per the ruling, the federal law that requires compulsory unionism in certain situations does not provide the unions with a means for forcing employees, over their objection, to support political causes which they oppose.
To the extent that this "union" is more of a PAC than a collective bargaining agreement over labor contracts, the specific protections (like required payment of dues) melt away.
[1] - https://legal-dictionary.thefreedictionary.com/trade+union
[2] - https://www.justfacts.com/unions.asp