The senate has summoned Godwin Emefiele, governor of the Central Bank of Nigeria (CBN); Adebayo Shittu, minister of communication, and Abubakar Malami, minister of justice over the reduction of MTN fine.
The Nigeria Communications Commission (NCC) had imposed a fine of N1.04trn on MTN for failing to disconnect millions of unregistered phone lines.
But after a series of horse-trading, the government reduced the fine to N330 billion, which the telecommunications giant agreed to pay.
However, the legislature said the federal government did not carry it along in the process of reducing the fine.
The house of representative had earlier probed the decision of the government to reduce the fine.
And on Thursday, the senate began its own investigation into the process by summoning the officials.
Gilbert Nnaji, a senator from Enugu east, brought the motion, which urged the senate to summon the key officials involved in the matter.
The CBN governor was joined in the summons because the money paid by MTN was allegedly remitted to an account of the apex bank where proceeds of corruption are deposited in.
Also, the minister of justice was summoned because of him being a key figure in the negotiation process.
Senate President Bukola Saraki directed the committee on communication, and justice to invite the officials and submit their report after two weeks.