BERLIN (Reuters) - Bayer on Tuesday hired law firm Sidley Austin to investigate a Europe-wide data collection scheme run by its Monsanto unit, which targeted journalists, politicians and other stakeholders to influence the debate on pesticides.

FILE PHOTO: The so-called "Chempark", the main plant and headquarters of German pharmaceutical and chemical maker Bayer AG is pictured along western Europe's most important waterway in Leverkusen, Germany, May 14, 2019. REUTERS/Wolfgang Rattay/File Photo

Bayer last week admitted that Monsanto, which it acquired for $63 billion last year, had gathered non-public information as part of the campaign, which French media said sought to influence the public debate on pesticides and genetically modified products.

Bayer faces potentially heavy litigation costs from U.S. lawsuits in which plaintiffs claim that its Roundup weedkiller, which contains glyphosate, causes cancer. Bayer disputes this.

In a Q&A document posted on its website on Tuesday, Bayer said U.S public relations and marketing agency FleishmanHillard, on behalf of Monsanto, had mapped stakeholders in France, Germany, Italy, Netherlands, Poland, Spain, and United Kingdom as well as stakeholders related to EU institutions.

Sidley Austin will investigate how many stakeholders were included in those files and whether people from other countries could also be affected, Bayer said.

The law firm would then contact affected people, most of them journalists, politicians and scientists, no later than by the end of the coming week.

French prosecutors said they had opened an inquiry after newspaper Le Monde filed a complaint alleging that Monsanto had kept a file of 200 names in hopes of influencing their positions.

Bayer has ended its PR collaboration with FleishmanHillard, but continues to work with the firm on marketing projects.

Bayer shares have shed more than 40 percent since a first adverse U.S. judgment on Roundup last August, leaving the company with a market capitalization smaller than the price it paid for Monsanto.

(This story removes reference to class-action lawsuits, paragraph 3)