In Australia this is called speculative invoicing, and its illegal. A company I was working for was doing SI for support contracts, regardless if the client was active with us or not and regardless of they even owned or used the tech that we supported.

My boss was just sending this shit out without telling the service department and without providing us a copy of the support contract and then we got angry calls from former clients and we didn't know why or what the support contract covered. Eventually I figured out what was going on, and when a call came in, I'd repeat the speil - the invoice is optional, it only covers X, if you dont have X then you dont need support for it, here's the phone number of the boss.

Sure enough, when the boss started getting angry phone calls while he was off fishing and treating his business like a passive income, he was angry at me.

He didnt fire me though, I eventually left and took a big chunk of his neglected legit clients.