Fall foul of somebody/something

Pro Tip 1/3

Used when someone does something against the law or formal rules.

If you copy someone else's work, you could fall foul of plagiarism laws.

Pro Tip 2/3

Implies that there will be negative outcomes, like fines or penalties.

Companies can fall foul of environmental regulations and face heavy fines.

Pro Tip 3/3

Often used as a cautionary advice to not break established norms.

Make sure to declare all your income to avoid falling foul of the taxation rules.