Italy's constitutional court has begun deciding whether Prime Minister Silvio Berlusconi's immunity from prosecution is legal.
Berlusconi says he is the victim of left-wing witch-hunt
A law passed by parliament earlier this year gave Mr Berlusconi immunity as long as he remains in office.
Critics claimed it was a deliberate attempt to scupper a corruption trial.
The trial in Milan relates to an alleged attempt to bribe judges during Mr Berlusconi's business dealings.
The constitutional court's 15 judges must reach a decision on whether the law should be upheld by 23 January, although court sources said an announcement could come next week.
Lawyers for Mr Berlusconi argued in court for the law to be retained.
Mr Berlusconi's chief lawyer, Gaetano Pecorella, said the court's ruling would have implications "beyond the Berlusconi case".
If the law is revoked, the Milan trial is expected to resume. If the law stays, it will be too late to restart proceedings by the time Mr Berlusconi's time in office has elapsed.
Milan prosecutors claim the law is "openly anti-constitutional" by changing the principle that all Italians are equal.
As well as covering Italy's prime minister, the law also grants immunity to the president, speakers of both houses of parliament, and the president of the constitutional court.
Mr Berlusconi, Italy's richest man, is believed to be worth more than 10 billion euros ($13 billion).
He claims the Milan trial is politically motivated.
Mr Berlusconi is accused of attempting to bribe judges to block the takeover of a firm by a business rival.