Corporations are fictional persons created by state statutes; and do not have rights of humans such as voting or influencing elections by spending money or otherwise. Nor can any corporation have a religion. Collective bargaining via unions is necessary for proper interstate and international commerce, including an absolute right of a bargaining unit to negotiate exclusion of non-union coworkers, to strike, and to hold secondary boycotts. Sites with multiple bargaining units, possibly of different unions may, by negotiation, reach an agreement with each union to coordinate strikes and other activity. This Amemdment imposes no negotiation duty or requirement upon unions, and state so-called right to work laws, however worded, are void as against public policy. Any spending by any collective or aggregation of money shall have to identify every contributor and amount of contribution in a publicly filed document open to public viewing. Citizenship is not a requirement for membership in a union. Federal and state law may reasonably regulate union pension funds for fiscal responsibly, but shall otherwise not interfere in union leadership and rank and file governance except for breach of criminal law or beach of safety or non-discrumination workplace regulatory law. Unions may not in concert with employers bargain to breach environmental protection law. Public and private sector workforces have equal union rights. Except as stated in this Amendment, no activity is exempt from union organization. Assertions of "national security" shall not be raised to inhibit freedom of action of unions. Upon passage of this Amendment all contrary existing law is void.
That's a start. Others more adept at saying the same thing more compactly and/or tying up loose ends should do their thing.
More reach may be advisable, but again, this is a first cut.