The supervisory board is meant to set the company's general agenda.
He was the only member of the 15-person supervisory board to do so.
The pay for sitting on a supervisory board is already public.
His future is expected to be decided on Tuesday at a meeting of the company's 20-member supervisory board.
For companies with 500-2000 employees, one third of the supervisory board must be elected.
From 1952 to 1966, he also sat on the supervisory board.
"That did not sit well with the supervisory board," he added.
The director is elected by the supervisory board for a period of three years.
After approval, only union members would be able to vote for candidates to the supervisory board.
He had been under mounting pressure to leave, even from other members of the company's supervisory board.