My “employer” (not really, but someone I work for) recently gave me a laptop to use for his business, something I had requested so I would keep my activity for him as separate as possible from my personal work or work for other clients.
I doubt that he installed any spyware on this computer, but I believe in taking no chances, so I wiped out the entire OS and reinstalled it from scratch**, just in case. No matter how justified it might be, there is nothing in my contract that permits such monitoring, clandestine or otherwise.
** I am aware that some rootkit software can survive an OS reinstall, so I replaced the main boot drive with one of mine first.