Breaking the rules around staff working after 9pm has cost French supermarket Monoprix dear.

The country’s leading trade union CGT took Monoprix to court for failing to respect a 2013 court decision that effectively barred the company from opening after 9pm.

Monoprix were supposed to enter into negotiations with trade unions to draw up a new agreement over working hours and conditions.

If an agreement was not forthcoming the company would be liable to a fine of €5,000 per infringement if it opened after 9pm.

But that didn't seem to bother the supermarket giant and this week a court of appeal decided to punish Monoprix for its “resistance” by setting a formal fine.

For not sticking to the rules  the court settled on a final penalty of €750, 000, a third of which will have to be paid up front.

Monoprix must also hand over €10,000 a day for any time it commits an offence by keeping a store open after 9pm in future.

The fine is just the latest incident in a battle between stores in France and trade unions over late night working hours.

Employee unions in France have in recent years intensified their legal efforts to protect the ban on nocturnal working hours, targeting major retail chains

In recent years retail giants such as Sephora and Apple have been stung by French courts for keeping their stores open after 9pm.

Eric Sherrer from the CLIC-P trade union that represents shopworkers has told The Local that he does not want to see Paris turn into New York, with shops open all night.

“France is already the most visited country in the world. Tourists come here for the culture not just for the commerce,” he said.

The law about opening late in France is there because we think it is necessary. It's not a case of having important rules and less important rules, a law is a law and it needs to be respected.

I don’t care if you can go to the Apple store or Sephora store in New York at any time of the night. If they respect the laws there, good for them, but this is France.”