bb says Since the Internet does not have "right to work" rules, only those members in good standing will be permitted to post political comments henceforth.
Right to work laws in the US are STATE LAWS that say that the company may hire workers who do not choose to be voting members of the union or to pay dues to a union.
Some STATES allow workers at a company to "not be members" but allow the union to require them to pay dues. The proper terminology here is a "Union Shop," and all represented employees pay for representation, but don't necessarily have to be members of the union. The collection of dues for non-members can be by payroll deduction if the contract includes a "check-off" clause (which is illegal in most "right to work" states.)
A few states have passed STATE LAWS enabling union contracts to require all employees in a bargaining unit to actually be union members in good standing, and this is called a CLOSED SHOP provision of State Law. A company can only be prevented from hiring anyone they like, regardless of union membership, only in the few "Closed Shop" states, and even then only if the membership requirement is included in the contract.
FEDERAL LAW requires that a union must provide full representation for all members of the bargaining unit regardless of whether they choose to be "voting members" and regardless of whether they pay dues, so in any case non-members who "are part of the group" for which the union has reponsibility have all the rights of others, regardless of payment of dues and regardless of participation in union votes. The only way of avoiding giving rights to non-members is to exclude them from getting a job within the bargaining unit, legal only in the few "Closed Shop" states and then only at companies who have agreed with a closed shop clause in their contract with the union.
Aside from voting, a US union may offer "side benefits," like a discount agreements with local merchants, or in fairly rare cases "sponsored (discounted) auto insurance," etc., that come only with the "union card;" but all rights defined in the contract are - by FEDERAL LAW SUPERCEDING STATE LAWS - shared by all in the defined group of employess and the union IS REQUIRED to assure enforcement and delivery of the terms of the contract to all.
As "posting" is a legitimate work task here, a citation of the specific (state) law permitting a Closed Shop, and a copy of the required written and approved contract showing inclusion of a membership requirement and current validity of the contract for the membership will be necessary before implementing bb's claim of his restriction (for US members at least).
(But calling the non-members "SCABS" is a surviving tradition, although "free riders" is more common in some places due to PC.)