Germany's president has sparked a row by saying the state should not try to level out living conditions between the west and the former communist east.
Mr Koehler's job is largely ceremonial
Horst Koehler told Focus magazine that there was a danger that poorer regions would become dependent on subsidies.
Several politicians accused Mr Koehler of undermining German unity, but others praised him for speaking his mind.
Mr Koehler's comments broke Germany's national taboo, nearly 15 years after the 1989 reunification, analysts say.
The promise that the east would one day be as prosperous as the west was a central theme of the reunification.
The failure to achieve parity despite huge subsidies is an embarrassment, the BBC's Ray Furlong in Berlin says.
In an interview with Focus magazine, Mr Koehler said there would always be differences in living standards in different parts of Germany.
People in eastern Germany have staged rallies against welfare cuts
"There were and are everywhere in the republic large differences in living standards - that is true from north to south and from east to west," he said.
"If you want to level them out, you cement the subsidised state and place an intolerable burden of debt on the young generation... We must get away from the subsidised state."
Mr Koehler also urged eastern Germany's unemployed to show greater flexibility in their search for work.
Though the president also mentioned the north-south differences, his comments were widely taken as aimed specifically at the east, where incomes remain lower than in the west and where unemployment is almost twice as high, analysts say.
"The message that comes across to east Germans: be satisfied, there won't be any more equality," the head of the Green Party, Reinhard Buetikofer, was quoted as saying by the Associated Press news agency.
Several other politicians said the president's remarks would only reinforce the position of the former communists in this weekend's regional elections in two eastern states - Brandenburg and Saxony.
But some defended Mr Koehler - a former International Monetary Fund chief - for what they described as honest remarks and a more realistic assessment of what is possible in Germany.
Premier of North Rhine-Westphalia Peer Steinbrueck said his state was facing huge financial burdens because of subsidies to eastern Germany.
Germany's press was also divided over the president's remarks.
"Koehler - president of all Wessis!" read the banner headline in the Berliner Kurier newspaper, which portrays itself as a champion of all things east German.
The terms "Wessis" and "Ossis" are derogatory nicknames for west and east Germans.
Meanwhile, Die Welt newspaper said the president was right.
"It is logical that it will not be possible to create the same living conditions in every place and every region in our country," it said.