Vodafone is suing the Italian telecoms company, Telecom Italia, claiming that it abused its dominant position in its home market.
Vodafone's Italian subsidiary is seeking damages of more than 1bn euros ($1.3bn).
Vodafone claims Telecom Italia committed abuses between 2008 and 2013, "with the intention and effect of impeding growth in competition in the Italian fixed-line market."
Telecom Italia has rejected the claim.
Italy's competition authorities fined Telecom Italia 104m euros ($138m) back in May for abusing its dominant market position.
Telecom Italia, which runs Italy's biggest fixed-line telephone network, said it will appeal against the fine.