The state is seeking to protect consumers and their wallets against deceptive packaging, although some retailers are critical.
ADVERTISEMENTSupermarkets will now have to inform their clients when a product is a victim of "shrinkflation".
This means that the amount of goods being offered is lower than previously while the price stays the same, or rises.
As of the start of this week, retailers are required to place visible labels on these products, according to a ministerial order published on 16 April.
Shops with an area smaller than 400m² are exempt from the ruling, which also only concerns products that are marketed at a constant quantity.
This excludes loose goods, as well as products that are packaged at the counter such as cheese and meat cuts.
Breaches of the new rule could incur a fine of €3,000 for an individual - the manager of a shop, for example - and up to €15,000 for a corporation.
"Shrinkflation is a rip-off, we're putting an end to it. I want to rebuild consumers' confidence and confidence goes hand in hand with transparency," said Finance Minister Bruno Le Maire.
The measure aims to give consumers greater knowledge and control over their purchasing power.
Last year, the price of food products became an important talking point in France when food inflation hit a record 16%, although this figure has since dropped to 0.8%.
French supermarket Carrefour, which has previously been criticised for shrinkflation, recently told BFM Business that there would be no need for the stickers in its stores.
"To combat shrinkflation and not penalise customers, the group has implemented a strategy aimed at identifying any products affected by this practice, so that their price can be corrected in advance with its suppliers and its pricing policy," a Carrefour spokesperson told BFM.
The new decree would encourage suppliers to make sure that pricing is fair, the firm added.
Retailer cooperative Système U has been more critical of the policy.
"If a decree materialises, we will respect it and apply it, but we’re not happy about it," CEO Dominique Schelcher said in January.
Michel-Edouard Leclerc, President of the E.Leclerc cooperative, has also shown his opposition to the new rule.
"It's the manufacturer who knows that his product has been reduced in size," he said. "It's up to the manufacturer to write it on the packaging."
He suggested that it would be a waste of time for supermarkets to apply stickers to affected products.
