The local units of Orange and MTN owe Cameroon nearly 100 billion CFA francs ($166 million) in unpaid taxes, including on games, the Central African nation's corruption board said on Wednesday.
A wide-reaching probe into the telecoms sector, carried out by anti-corruption commission CONAC, found that taxes totalling 176 billion CFA francs had gone unpaid from various companies, also including Camtel and Viettel.
The amount paid by each company was not clear and the companies were not immediately available for comment.
The report is another blow for MTN, which is already contesting a $3.9 billion fine in Nigeria for failing to disconnect users with unregistered SIM cards.
Unregistered SIM cards can be used for criminal activity - a growing concern in Nigeria facing the threat of militant Islamist group Boko Haram.
MTN successfully lobbied to get the fine reduced from $5.2 billion in December.