Italy’s antitrust authority said on Friday it had fined Italy’s top four phone operators a total of 228 million euros ($253 million) for breaching competition rules by collectively agreeing to raise their prices.

The watchdog opened a probe against Telecom Italia, Vodafone, CK Hutchison’s unit Wind Tre and Swisscom’s Fastweb in 2018, claiming the carriers had agreed to raise tariffs after they had been forced to scrap a billing scheme based on 28 days rather than a full month.

Italian consumer association Altroconsumo, which campaigned against the companies’ billing practices, said the fines were equal to 114 million euros for Telecom Italia, 60 million euros for Vodafone, 39 million euros for Wind Tre and the rest for Fastweb.

The antitrust decision could be appealed by the companies.