Italian police have been carrying out checks at the Milan offices of Facebook to assess whether it regularly declared its income in Italy, an investigative source and the U.S. company said on Friday.
Italian officials have stepped up their efforts to collect taxes in recent months and have already targeted other big corporate names such as Google to check whether they are paying their dues.
The investigative source said tax officials first went to the offices of Facebook in Milan nearly a month ago to collect documents.
"Facebook pays taxes in Italy as part of its business activity in the country and strictly complies with Italy's fiscal rules," Facebook said in an emailed statement.
"Facebook has fully cooperated with tax police during the investigation and intends to continue to do that."
Italian police opened a new tax probe into Google Italy last week, five years after an earlier investigation into transfer pricing.
Google has said it complies with the tax laws in every country in which it operates.