I'm not saying people aren't allowed to oppose unions, either ideologically or legally. If a jobsite is trying to organize, employees discussing "individual agency" is fine. But there are only 2 competing ideologies "union" or "no union".

There are plenty of people who would accept the viewpoint that members of the labor unit cannot themselves engage in "union busting" because they aren't part of the management group (there would also be hardliners who feel that all people of all levels of the organization that undermine the union are attempting to union bust, myself among them, but I'm fine pointing out that there is another viewpoint)

That said, any action that an employer takes to prevent unionization, legal or illegal, fun or boring, is engaging in "union busting". They have ways in which they are legally allowed to do this, but any attempt to describe anti-unionizations efforts taken by management as somehow not being "union busting" is disingenuous based on the definition of the term.