The group's supervisory board met on Friday to discuss restructuring efforts, including a renewed push to divest Thyssenkrupp's steel division.

Attempts to list, spin off, sell or merge the cyclical steel division with a peer have failed in the past, mainly because of the billions of pension liabilities tied to the business that goes back more than 200 years.

The union is willing to examine a possible divestment of the steel business but the division must have the necessary financial resources, the union's letter, seen by Reuters, said.

"There is a lot of speculation in the press, but no concrete plans that we are aware of or that will be discussed with us. So nothing was decided!," the letter read.

The company declined to comment on the internal letter.

Thyssenkrupp CEO Martina Merz is under pressure to deliver on her pledge to slim down the group and revive its languishing share price.

Merz's concept of a "group of companies" had failed, the union said, adding there had been a lack of an overall concept from the supervisory board for months.

The union called on the board to examine which businesses could be developed on their own and what partners would be needed.

(Reporting by Christoph Steitz and Tom Kaeckenhoff; Writing by Riham Alkousaa; Editing by Jan Harvey)