"This law clearly discriminates against all those who before 1989 were outside the communist nomenclature," Adam Michnik, editor of the daily Gazeta Wyborcza, wrote.
President Aleksander Kwasniewski, himself a former communist, signed the civil service law on Tuesday, even though he agreed with opposition charges that it contained flaws.
The measure, linked to a wider administrative reform, aims to guarantee that officials are properly qualified.
But it rules that top officials must have seven years' experience, including four years in managerial posts - leading critics to accuse the ruling ex-communist Democratic Left Alliance (SLD) of blocking those who were not part of the pre-1989 communist system.
They also object to a provision that graduates of a special national college, founded in the early 1990s to train civil servants for democratic Poland, will not qualify for higher posts.
"This law is clearly bad as it puts people from the old system into privileged positions," said Andrzej Potocki, spokesman of the centrist opposition, Union for Freedom.
Mr Kwasniewski, who is close to the SLD he once led, acknowledged that there were problems with the otherwise necessary law and wrote to parliament suggesting changes before it takes effect on 1 January.
Mr Potocki said that his party would accordingly have an amendment to the law ready this week.
"We will propose limiting the required period in office from seven to three years, including a requirement for knowledge of foreign languages among lower officials, and allowing graduates of the National School of Public Administration to attain high posts," he said.
Dariusz Klimaszewski, press liaison officer for the SLD's core party, said the charges of favouring ex-communists were unfounded as veterans of the old system were retiring anyway.
He said there might be a case for introducing a fast-track for talented young people to senior jobs, but he attacked the outspoken criticism of the new law. "To portray something which is an evident success as a bad measure is simply not fair," he said.Reuse content