In France as in most of Europe the law usually mandates at least 1 day off per week and this day off is not a matter of personal choice: you *have* to take the day off.This from the country that fined a baker 3,000 euros because he opened 7 days a week during peak visitor season.
Usually there are some special permits granted for specific jobs or specific situations like tourism or some events happening etc... but if the permit is not granted you cannot just decide to stay open outside of the legal limits and expect no consequences.