Tax code violations, for sure. Environmental regulations may also carry huge maximal fines. Some misdeeds can even lead to criminal prosecution and land you in jail (but generally, they won't, except for the worst of transgressions).
Note that the GDPR requires fines to be proportional to the offence. If you really worry about some regulator fining you for 20M euros just because they're having a bad day, you do have legal recourse available.