* VW installs new board members ahead of May 5 AGM
* Piech challenges VW's board choices -Bild
* VW, Piech's office, Porsche SE, IG Metall decline comment (Adds Bild report and background)
By Andreas Cremer and Jan Schwartz
BERLIN, April 30 (Reuters) - Volkswagen and newly departed chairman Ferdinand Piech clashed again on Thursday over supervisory board appointments, causing new strains at the carmaker ahead of what is likely to become a tense shareholder meeting next Tuesday.
Piech, a dominant figure at VW for more than two decades, quit last Saturday after a damaging showdown with Chief Executive Martin Winterkorn at a time when VW is posting higher profits and pushing cost cuts.
Europe's largest automaker on Thursday sought to regain the initiative by appointing two members of the Piech family to its supervisory board, filling vacancies left by Piech and his wife Ursula who had also quit the 20-seat panel.
Louise Kiesling, Piech's niece, and Julia Kuhn-Piech, a board member at truckmaker MAN SE and also a member of the Piech family took up their posts on Thursday after being appointed by a court in Braunschweig, Germany, VW said.
The Piech family and the Porsche clan together hold a majority of voting shares in VW through the Porsche SE holding company.
But Piech is challenging VW's choice and instead nominated long-time automotive manager Wolfgang Reitzle - seen as a potential replacement chairman - and former Siemens manager Brigitte Ederer, German daily newspaper Bild said.
VW, Piech's office in Salzburg, Porsche SE and the IG Metall union all declined to comment.
In Germany any shareholder, the works council and the company itself are entitled to nominate a new member to fill a vacancy on the supervisory board via a court, a source familiar with the matter told Reuters, citing the law on stock companies. The company is the only party of the three obliged to do so, he added.
For Piech the only way to thwart the VW appointments would be to bring legal action against the court ruling, the source said.
The Bild report suggested Piech is contemplating legal action against his own relatives in addition to already being at odds with Wolfgang Porsche, his cousin and chairman of Porsche SE, who sided with labour leaders and the governor of Lower Saxony in forcing Piech to resign.
Piech's departure has left a void at the top of Europe's largest automaker and a host of questions about its future are expected to be aired at the annual meeting on May 5.
In the interim former IG Metall union boss Berthold Huber has replaced Piech as head of the supervisory board, which is evenly split between stakeholder and labour representatives.
"The search for a successor to Piech at the top of the supervisory board has the utmost priority for investors," said Ingo Speich, a fund manager at Union Investment which holds 0.6 percent of VW preference shares. (Additional reporting by Georgina Prodhan.; Editing by Greg Mahlich)