Germany's ruling party and Jewish groups have criticised the conservative opposition's selection of a Nazi-era judge to help elect a new president.
Mr Filbinger is accused of trying to defend Hitler's dictatorship
The Christian Democratic Union (CDU) chose Hans Filbinger to sit on the assembly selecting the next president.
The 90-year-old is a former military judge accused of ordering the execution of German deserters in World War II.
Chancellor Gerhard Schroeder's Social Democrats and the leaders of Germany's Jewish groups criticised the CDU move.
"This is a tasteless act," said Klaus Uwe Benneter, a deputy leader of the Social Democrats, on German TV.
"No-one will ever forget his past as a terrible judge..." said government spokesman Thomas Steg.
"I cannot understand why the CDU has decided to send him," said Paul Spiegel, a Germany Jewish community leader also sitting on the special federal assembly.
"There are surely other worthy candidates without a past like this."
The Nazi-hunting Simon Wiesenthal Center in America launched an online petition calling for his removal as an elector.
But CDU leader Angela Merkel said she found the outcry "puzzling".
"I don't understand why he's being criticised," she said, adding that he had been on a number of previous federal assemblies.
Mr Filbinger was forced to resign as the premier of Baden-Wuerttemberg state in 1978 after he was quoted as saying of Hitler's dictatorship, "what was right then cannot be wrong now".
The comments sparked a furore, but he claims they were taken out of context.
He also insisted he never actively sentenced anyone to death, and in fact saved lives by handing out mild verdicts.
The federal assembly, which selects the president, is made up of
1,205 people. Around half are from the Bundestag lower house of parliament, and the rest are chosen by state parliaments.
It was the CDU in Baden-Wuerttemberg who chose him to sit on the assembly.
Despite the row, CDU candidate Horst Koehler is expected to beat Mr Schroeder's nominee Gesine Swan
as the CDU and its allies have a majority of seats.