You’d explicitly ask your HR department in writing, and get your Work Number report from Equifax (you can get it, right?) to make sure your employer isn’t mistakenly/maliciously sending data over despite claiming not to.

Both of those are post-hire actions, and assume that you will get an accurate response from either party.

Yeah I asked at my last place and they were basically like “too bad it’s not changing”

If you are able to resign, it will make them reconsider this decision.

I did, for various reasons including that

True, but presumably the next time you are interviewing for a job, you can ask during the interview process, and then terminate the process of they tell you they do it. Preferably after they've wasted a bunch of time and money on your interviews.

See my answer here: https://news.ycombinator.com/item?id=33214006