The so-called "Duplomb law" has stirred public anger for permitting a return of acetamiprid -- a chemical known to be toxic to pollinators such as bees and to ecosystems. It was adopted on July 8 but has not yet come into effect.

The legislation, named after the conservative lawmaker who proposed it, was presented in parliament as a measure to "reduce constraints" on French farmers.

But its move to bring back acetamiprid prompted a 23-year-old master's student to launch a petition against it which quickly snowballed, gathering support from many people, including actors and several leftwing lawmakers.

The French parliament's official website showed it had accumulated more signatures than any other. At 8:30 pm (1830 GMT) Saturday the counter had passed 620,000.

The petition's author, Eleonore Pattery, who describes herself as "a future environmental health professional", called the new law a "scientific, ethical, environmental and public health aberration".

"It represents a frontal attack on public health, biodiversity, the coherence of climate policies, food security, and common sense," she said.

- A 'bee killer' -

Acetamiprid has been banned in France since 2018, but remains legal within the European Union.

The insecticide is particularly sought after by beet and hazelnut growers, who say they have no alternative against pests and face unfair competition.

On the other hand, beekeepers have described the chemical as "a bee killer".

Its effects on humans are also a source of concern but, in the absence of large-scale studies, its risks remain unclear.

The petition calls for the "immediate repeal" of the law and a "citizen-led consultation involving health, agricultural, environmental and legal stakeholders".

Petitions do not in themselves trigger a review or repeal of the legislation but unprecedented public support may prompt renewed parliamentary discussion on the matter.

Under French rules, if a petition reaches 500,000 verified signatures, the National Assembly may choose to hold a public debate limited to the content of the petition itself.

In late June, before the law's passage, several thousand demonstrators - including farmers, environmental organisations and scientists - rallied across France calling for the bill to be withdrawn.