talking-to
A serious warning talk about your bad behavior.
A talking-to is a serious conversation where someone in authority corrects you or warns you about your behavior. When your teacher gives you a talking-to about not turning in homework, or your coach gives the team a talking-to about their lack of effort at practice, they're making it clear that something needs to change and that your behavior has consequences.
A talking-to isn't quite as severe as formal punishment, but it's definitely more serious than a gentle reminder. It sits somewhere between a friendly suggestion and real consequences. Your parents might give you a stern talking-to about leaving your bike in the driveway again, or a librarian might give students a talking-to about being too loud.
The phrase suggests that the person doing the talking has more power or authority in the situation, and the person receiving it is expected to listen and improve. After a talking-to, you usually understand that you've been warned: if the behavior continues, bigger consequences may follow.