Except the stated goal of European Union is free movement of workers. You can literaly go and work in any EU country, no visa or work permission needed. But th

Except the stated goal of European Union is free movement of workers. You can literaly go and work in any EU country, no visa or work permission needed. But that's not really the situation here: it's a business providing services for customers in another country. You send a driver abroad for a few days, that should not make him subject for local tax and labor laws. If you can prove that said worker spent significant period of time there (most tax treaties use 183 days as a rule of thumb) then that's a different matter.