If I understand the problem correctly, VW doesn’t want unionization, they want a workers council, whatever that is. Under US law for some reason, a car plant that isn’t unionized can’t have a workers council. On top of that, a car plant can’t apparently unionize unless they do it under the UAW.
In other words, VW doesn’t “want” the union, it wants the freedom to be a more responsive company to its workers, a freedom currently outlawed by the US government unless the UAW gets its cut first.