The two billionaire media tycoons have been involved in a series of disputes
Rupert Murdoch's News Corp is suing two units of Silvio Berlusconi's Italian broadcaster Mediaset.
News Corp said that the Italian prime minister's media arm was preventing its Italian unit, Sky Italia, from buying ads on its television networks.
"News Corp believes these companies have violated European Commission rules governing free competition," it said.
Mediaset has recently expanded into pay television, which was formerly solely the domain of Sky Italia.
News Corp said that Mediaset was stopping it from buying ads on Mediaset's free-to-air networks - Canale 5, Italia 1 and Rete 4.
Mr Berlusconi is among Italy's richest men, estimated to be worth $6.5bn (£4.4bn) by Forbes magazine. Now serving his third term as Italy's prime minister, he controls Mediaset as well as AC Milan football club.
Mr Berlusconi has recently accused fellow billionaire media tycoon Mr Murdoch of mounting a personal attack on him via The Times newspaper over several scandals involving his private life.
His lawyer said he planned to sue newspapers in the UK, as well as across Europe, for libel.
News Corp, run by Mr Murdoch, owns pay TV broadcaster Sky as well as the Times and Sun newspapers in the UK and the New York Post and Wall Street Journal in the US.