The firm, now owned by German chemical giant Bayer, failed to inform the people on the watch lists compiled in the context of a heated public debate about glyphosate, a weed killer, it ruled.

The CNIL agency fined Monsanto 400,000 euros ($473,000) in the case brought by seven plaintiffs.

Compiling lists of contacts was not in itself illegal, the agency said, but only people who could "reasonably expect" to figure on such lists because of their business sector or their public standing should have been included.

Furthermore, data had to be collected legally and targets informed, including of their right to refuse being listed. By keeping the lists secret, Monsanto deprived them of this right, CNIL said.

Monsanto gave a rating of one to five to each of the over 200 people on its French lists corresponding to their estimated influence, credibility and level of support for Monsanto on several topics, especially pesticides and genetically modified crops.

The case, first reported by French media Le Monde and France 2 television in 2019, quickly spread to other European countries where Monsanto was also keeping lists.

Lawyers hired by Bayer -- which had acquired Monsanto the previous year -- said that they found close to 1,500 politicians, journalists and others "located primarily within the EU"