They see Tesla as a threat to their system as Tesla is the only in the US not part of it and they are doing better than all the other car companies.
I know someone who saved companies from bankruptcy, usually heavy industries. When he get hired he install security cameras and other measures and after a few week usually find out that a lot of people are constantly stealing valuable materials from the company. It’s always people in the union with some friends that work on the floor.
He confront them, fire them and a few months later the company become viable again. He found out that the most corrupt people are almost always in the Union organisation.