Senator Dino Melaye, who made the allegation in a motion submitted to the upper house, said $13.92 billion had been repatriated “illegally” out of Nigeria by MTN through its bankers between 2006 and 2016.
The investigation threatens to raise tensions between Nigeria and the South African firm just three months after MTN agreed to pay a reduced fine of 330 billion naira ($1.05 billion) in a settlement with the government over unregistered SIM cards.
The move comes as Nigeria, Africa’s biggest economy, is in recession for the first time in more than 20 years.
However, MTN has declined to comment on the decision of the Senate to investigate it. MTN which is the largest mobile phone operator in Nigeria accounts for around one third of the company’s revenues. The telecom giant had threatened to pull out of Nigeria during the dispute over unregistered SIM cards.
The upper house agreed that its committee on banking, insurance and other financial institutions would “carry out a holistic investigation into the matter and report back to the Senate”.