FRANKFURT/DUESSELDORF (Reuters) - Thyssenkrupp's deputy chairman will vote against the contract extension of CEO Miguel Lopez at a board meeting on Friday, saying he had not delivered a promised turnaround of the steel unit after selling a stake to billionaire Daniel Kretinsky.

The comments by Juergen Kerner, one of Germany's most influential labour representatives, mark a major escalation in the conflict between management and workers over the German conglomerate's restructuring, notably its steel division, which the group has sought to divest for years.

It is also a rare display of CEO opposition at the top boardroom level in Germany, whose corporate culture relies on consensus between shareholder representatives and powerful labour unions.

Thyssenkrupp referred to earlier comments by Lopez that a restructuring of the group's steel business was a top priority.

Thyssenkrupp's supervisory board will convene on Friday to vote on a planned spin-off of its warship division TKMS as well as a new contract for Lopez, who took over two years ago, sources said last week.

Kerner warned of massive resistance if Lopez's contract extension went through against the will of worker representatives, which can only happen via a decisive vote by chairman and former Siemens manager Siegfried Russwurm.

Kerner, deputy chief of Germany's biggest union IG Metall, who also sits on the supervisory boards of Siemens, Siemens Energy and Traton, told Reuters that while he and Lopez had established a working relationship, "we now have a fundamental mistrust on both sides".

He said workers could use the means at their disposal, including strike action, going forward unless Thyssenkrupp was able to draw up a convincing future plan for the steel division and sufficient funding, which he described as red lines.

Kretinsky, who acquired a 20% stake in TKSE last year and is reportedly considering increasing his share to 50%, has declined to engage with employees regarding his vision for the company's future, Kerner said. This reluctance, Kerner said, makes him an unsuitable partner.

"We have officially asked Mr Kretinsky for talks, both verbally and in writing and via WhatsApp. We always receive a very friendly reply that he would like to talk to us at a suitable time, but that he is currently unable to make a statement," Kerner said.

"In my view, this is unacceptable."

A spokesperson for Kretinsky's EP Group had no immediate comment.