Heinrich von Pierer, one of Germany's top business figureheads, is coming under mounting pressure from other members of Siemens (NYSE: SI - News) ' supervisory board to resign from his post as chairman of Europe's biggest engineering group.

Twin scandals engulfing Siemens, involving alleged bribery and the alleged financing of a rival to its main union, are making several directors, on both the labour and capital sides, nervous. The acts under suspicion mainly took place during Mr von Pierer's time as chief executive.

A forced resignation would mark an ignominious end to the career of one of Germany's most prominent businessmen. He not only led Siemens for 13 years but also advised several of the country's chancellors and sat on supervisory boards at Volkswagen and Deutsche Bank.

People close to Mr von Pierer, who denies any knowledge or wrongdoing, said he was "ready to fight". They said he "saw no reason to give up his office early" but left open whether he could do so when his post comes up for renewal in January.

A person close to the supervisory board said: "The internal and external pressure is growing on him. The noise is increasing from the government in Berlin as well as the Bavarian government [where Siemens is based]. At a certain point, you can't survive that pressure any more."

Supervisory board members favour Gerhard Cromme, chairman of steelmaker Thyssen-Krupp, as the next chairman as he is in charge of Siemens' audit committee, which is leading the investigation into the scandals.

"Cromme is the natural choice as he has the most insight of all the outsiders on the board," said one person close to Mr von Pierer. The push in calling for Mr von Pierer's scalp is coming from IG Metall, the engineering union that is under pressure from the scandals. The union has called for prosecutors to investigate whether Siemens indirectly but illegally helped finance a rival organisation, the AUB.

Most, but not all, of the 10 members representing the capital side of the board would wait for the outcome of the investigations – both internal and by prosecutors – before calling for resignations, people close to the board said. A solution was expected by the middle of the year, possibly by the next board meeting on April 25, they added.

Siemens denies any wrongdoing in the bribery scandal and says any responsibility lies with a rogue group of employees. It says it is co-operating with prosecutors in the AUB scandal to clear up as quickly as possible what happened.