An ouster of Winkeljohann, who won wide investor praise for securing former Roche executive Bill Anderson as Bayer's CEO-designate, could add to upheaval at the company, which has attracted activist shareholders and is facing costly litigation.

DWS, Union Investment and Deka Investment said they would not vote for the supervisory board chairman when his term comes up for renewal at the healthcare and agriculture group's annual shareholder meeting on Friday.

Union Investment has previously come out saying it would not back the re-election but the other two mutual fund firms had not previously disclosed their voting intentions.

Major shareholder advisory firms Glass Lewis and Institutional Shareholder Services (ISS), for their part, have said they would back Winkeljohann, without elaborating on their reasons.

In a further sign of investor support in the run-up to the AGM, German weekly magazine WirtschaftsWoche this month cited unnamed sources as saying that Singapore's sovereign wealth fund Temasek, a major shareholder in Bayer, would vote for Winkeljohann.

A former head of six European countries at auditing and consulting firm PwC, Winkeljohann has chaired Bayer's non-executive board since 2020.

But he is also Deutsche Bank's deputy chairman, chairman at unlisted wholesale trade groups Sievert SE and Bohnenkamp AG as well as a board member at steelmaker Georgsmarienhuette GmbH.

In its notice of the AGM, Bayer said the "supervisory board has satisfied itself" that Winkeljohann is able to make time for his duties, taking into account his seats on other boards.

(Reporting by Ludwig Burger; Editing by Rachel More and Susan Fenton)

By Patricia Weiss and Ludwig Burger