US tech giant Apple and Japanese printer maker Epson face growing legal pressure in France over alleged planned obsolescence in their products as consumer groups make use of the country's law against the practice.

The association Stop Planned Obsolescence (HOP or Halte a l'Obsolescence Programmee) said it had filed a complaint against Apple after the company admitted to intentionally slowing down its iPhones as they age.

"Apple has put in place a global program of planned obsolescence with a view to increasing its sales," the association said in a statement issued on Wednesday.

On Thursday, the group hailed a breakthrough in a separate case against printer manufacturers when prosecutors opened a probe into Epson over claims that it was tricking consumers into changing ink cartridges before they were empty.

"It's very good news. For the first time in France and to our knowledge in the world, judicial authorities of a country have taken up a case of planned obsolescence," the association's lawyer, Emile Meunier, told AFP.

Planned obsolescence is a widely criticised commercial practice in which manufacturers build in the expiry of their products so that consumers will be forced to replace them.

It is decried by consumer groups as being unethical and is suspected of being particularly prevalent in the electronics industry, which produces mountains of unrecyclable waste each year.

- 'Hamon's law' -

To tackle the problem, France passed landmark legislation in 2015 known as "Hamon's law" which made the practice illegal and -- in theory -- obliged retailers to say whether replacement parts were available.

The law stipulates that a company found to be deliberately shortening the life of its products can be fined up to five percent of its annual sales while executives can face up to two years in jail.

The Epson case -- if the initial legal inquiry finds enough evidence for a trial -- could lead to the first prosecution for planned obsolescence, which lawyers warn is a difficult charge to prove in court.

HOP filed a legal complaint against printer manufacturers Canon, HP, Brother and Epson in September, claiming that their devices forced users to change their ink cartridges before they were empty.

Printer companies earn far higher margins on replacement cartridges than on printers, which are often sold cheaply.

Earlier this month, Apple confirmed what critics had suspected for years: that it intentionally slows performance of older iPhones as their batteries weaken from age.

The company said this was to extend the performance of the phone, which uses less power when running at slower speeds, and was to prevent unexpected shutdowns due to a low battery charge.

Critics accused it of nudging iPhone users to upgrade to newer models by letting them think it was the handsets that needed replacing, rather than just the battery.