WTW for someone agreeing to do something but it affects you

I remember seeing the definition on Google’s dictionary months back, but I can only vaguely remember it and the word. It’s like two parties agree (formally like signatures and stuff or informally I forget) on something, but it affects a third party (like you for example) who didn’t have a say in it.

I asked ChatGPT for help concerning this, and it said “unauthorized representation” or “unauthorized agreement,” which is not the word I’m looking for (it’s not even a single word). Anyways, I’m lost, and help would greatly be appreciated. Thank you.