Union busting is already illegal, and corporations have been getting away with it the entire time because there is essentially zero enforcement 99% of the time, and even in the rare cases where there is enforcement the penalties are 1/1000th the cost of unionisation. There’s no reason this will change.

I imagine proving union “busting” intent is also very difficult, as they use various tactics that could be considered standard practice in the eyes of the law (e.g. closing stores).