A GAS fine (sanction administrative communale / gemeentelijke administratieve sanctie) is a penalty a municipality can impose directly for minor nuisances — wrong parking, littering, noise — without going through a court. They are common and often contestable.
Who decides
A "sanctioning official" (fonctionnaire sanctionnateur / sanctionerend ambtenaar) handles the file, not the police and not a judge. That is who you write to.
The deadline
You typically have 15 to 30 days to send your defence in writing, depending on the infraction. The exact deadline is on your notice — follow it to the day.
How to contest
It is recommended to send your objection by email, fax or registered mail so you keep proof of sending. State your reference number, explain factually why the sanction is wrong or disproportionate, and attach any evidence (photos, tickets, permits).
If it is rejected
If the sanctioning official maintains the fine, you receive a reasoned decision and a new payment deadline. If you still disagree, you can bring the matter before the Police Court within one month. For small amounts this is rarely worth it, but the written objection itself is free and often enough.