A prosecutor on Monday lodged a request for Italy's former prime minister Silvio Berlusconi to stand trial immediately over accusations that he bribed a leftwing senator in 2006.
Italian law allows prosecutors to request immediate trial when the evidence of the crime is considered "obvious".
Prosecutors believe the media baron paid senator Sergio De Gregorio three million euros ($3.9 million).
The case goes back to parliamentary elections won by a centre-left coalition led by Romano Prodi by just a handful of votes.
A few months later, De Gregorio crossed the aisle and joined the Berlusconi opposition in a move that helped bring down the Prodi government in 2008.
The subsequent elections were won handily by Berlusconi.
The investigation is being handled by prosecutors in the southern city of Naples since that was De Gregorio's seat.
Media reports said five prosecutors including anti-mafia investigators were in charge of the probe.
The scandal-tainted Berlusconi, 76, has often been accused of buying votes or bribing lawmakers, but this is the first time he is officially under investigation for allegedly corrupting a politician.
The billionaire tycoon has been a defendant in multiple court cases but so far has only one outstanding conviction for tax fraud, which he is appealing.
He is also on trial for allegedly having sex with an underage prostitute when he was still prime minister and abusing the powers of his office.
Rules for "immediate trial" require a judge to decide within at most 10 days whether to order the trial.
If the judge agrees, the rules allow for the scrapping of preliminary hearings that could last more than a year.