crack down
crack down {v. phr.}, {informal}
To enforce laws or rules strictly; require full obedience to a rule.
After a speeding driver hit a child, the police cracked down.
- Often used with "on".
Police suddenly cracked down on the selling of liquors to minors.
The coach cracked down on the players when he found they had not been obeying the training rules.
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Source: A Dictionary of American Idioms