Altice's Lisbon headquarters and the home of the 71-year-old millionaire in Portugal's northern municipality of Vieira do Minho were raided by officers, according to broadcasters CNN Portugal and SIC TV.
Altice Portugal, which did not immediately reply to a request for comment, is the country's largest telecoms company and is part of the Dutch-based telecoms and cable group Altice.
In a statement, Portugal's department of investigation and criminal action (DCIAP) said 90 raids were conducted on Thursday and Friday at homes, companies and law firms across the country, and that three people were detained.
It did not name those detained.
It said it was investigating alleged crimes of corruption, tax fraud, forgery and money laundering.
"The suspicions that led to the investigations indicate that the Altice Group's decision-making process was rigged in terms of procurement, with practices that were harmful to the group's own companies and competitors," DCIAP said.
Those detained would appear in court on Saturday, it said.
DCIAP said documents and possessions, such as luxury cars, were seized, with an estimated value of around 20 million euros ($22.45 million).
SIC Notícias reported that Pereira was detained at a facility of the Portuguese criminal investigation agency (PJ) in Lisbon. PJ did not immediately reply to a request for comment. ($1 = 0.8908 euros)
(Reporting by Patrícia Vicente Rua; Editing by Catarina Demony and Alex Richardson)
