A ruling requiring face coverings in shops, banks, covered markets or any other enclosed public space came into force in France today.
Anyone violating the rule is liable to pay a €135 fine.
Ministers accelerated the rule change because, even though the disease has abated nationwide, there have been localised flare-ups that sparked fears of a second wave.
More than 30,000 deaths in France have been linked to Covid-19.
Government edicts about wearing face coverings to curb the spread of Covid-19 have touched off fierce debate in the United States and elsewhere about civil liberties.
In France, most people accept them as a necessary tool to fight the epidemic.
Shoppers entering the bakery in Paris where Kalil Gaci works are taking the new rule in their stride.
"There's no problem in wearing one, I'm completely for it," said Elina Outh, a 22-year-old business student who called in to buy some of Mr Gaci's pastries.
"What's happening makes sense and I think it should have happened a long time ago."
At the covered market at La Baule-Escoublac, a resort on France's Atlantic coast, a sign was displayed reading: "Stop Coronavirus. The wearing of a mask is mandatory."
A fishmonger at the market, who gave his name as Gregory, said shoppers had been complying.
"Since lockdown, people in La Baule were used to almost always wearing a mask, so people are respecting the rules," he said.