Berlusconi denies he has done anything wrong

The law protects Prime Minister Silvio Berlusconi from prosecution as long as he remains in office.

It has effectively halted a corruption trial in which Mr Berlusconi is accused of trying to bribe judges.

Left-wing opponents of Mr Berlusconi were outraged at the new law, and now say they will attempt to raise enough signatures to force a referendum.

Opinion polls have suggested that two-thirds of Italians are against the law.

We must wage battle in Italy to ensure there is equal justice for all Marco Rizzo Communist leader

Under Italian law, if 500,000 people sign the petition, a referendum must follow.

The referendum move is being backed by members of the Communist Party, Greens and civil rights organisations, who have denounced the law as "shameful".

"We must wage battle in Italy to ensure there is equal justice for all," said communist leader Marco Rizzo.

The timing of the immunity law is seen as particularly significant, coming just before Mr Berlusconi leads Italy into its six-month presidency of the European Union.

Five protected

The law protects Italy's prime minister and four other top officials from criminal prosecution as long as they remain in office. Magistrates can investigate complaints but not bring them to trial.

The law was signed by Italian President Carlo Azeglio Ciampi at the weekend, three days after being passed overwhelmingly in the lower house of parliament.

Supporters of the immunity say it restores an earlier Italian law, and brings it into line with much of the rest of Europe.