drop the hammer (on someone or something)

To punish or deal with someone or something with great severity or ruthlessness. I can't sneak out—I'm already grounded, and my parents have sworn they'll drop the hammer if I break the rules again. Federal regulators indicated that they were ready to drop the hammer on loan sharks who were exploiting loopholes in existing financial law. A: "Wait, Mike got expelled?" B: "Yep. Apparently, the headmaster dropped the hammer on him after he was caught cheating on an exam."