Earlier quoted context omitted.
Have you ever done a background check with HireRight? They ask you for all of your previous companies and contact them to verify. I think there is an option not to call your current employer.
How far can you legally go with those in the US? Here in the EU at most you can ask if they worked there, nothing else.
But that signals to their current employer that they’re applying for other jobs. Unlike the EU, employers in the US can be retaliatory about that.