Yes it's true. But Toyota has a very unique culture in which management are more like coaches, and every single employee on the line is expected to continuously introduce improvements in the assembly line. In such an environment, the employees are highly empowered. So it is natural that they would resist any attempt to prevent direct communication between them and management. When a union takes charge it is legally not permissible for workers to directly talk to management and vice-versa; they have to go through the union.