Of course, the owners are not going to support restrictive labor relations laws that are directly aimed at reducing their private property and contracting right

Of course, the owners are not going to support restrictive labor relations laws that are directly aimed at reducing their private property and contracting rights in order to enable their employees to extract above-market wages from them. But it's pretty hard for owners to prevent this kind of outcome. You are legally restricted from exercising your right to free association and only employing people who oppose unions, if you ever become an owner.