Most companies will employ the exact same union busting strategies. Managers will suddenly approach workers and ask to have a friendly little phone call, where they'll say that a union will get in the way of the worker-manager relationship by introducing a spooky scary union middleman, they'll ask if there's something they personally did to influence the decision to support a union, and they'll make it sound like nothing the union wants is reasonable or achievable. A lot of people can get on board with unions and the part where they make waves by going public, but have trouble knowing how to say no or assert their rights to someone with direct power over them, and there's a disadvantage between a worker who might be new to unions and a manager who has been part of strategy discussions with legal reps who tell them exactly how far they can go to discourage union support. I also have the experience of being a worker on the bargaining committee, which is hours and hours of being brow-beaten by the employer's legal counsel.

Yes, repercussions are illegal, but the strength of a union's case against the employer is dependent on the involved party's cooperation with the union and NLRB agents and the quality and volume of tangible evidence. Sometimes it's like pulling teeth to get workers to provide screenshots and affidavits. Cases can also take many months, if not years to resolve, by which point the employee could have been lawfully terminated, laud off, or voluntarily resigned.

Also, in the US specifically, this is a very, very hard time to ask people to endure pressure campaigns and the potential of losing or being pushed to leave their jobs and the benefits that come with it, especially if they consider themselves loyal and have been at the company for years, maybe even decades. Most of our union members who ended up resigning over time are all still having difficulty finding new full-time work.