Nigeria's oil company illegally inflated funds it collected the subsidy scheme to 5.1 trillion Naira between and 2015.

Lawmakers, on Wednesday, said they uncovered this allegation and they want it investigated.

The Senate's decision to look into the claim followed an emergency motion raised during plenary. Senator Dino Melaye, who told the Senate there were possible irregularities in subsidies collected by NNPC between 2006 and 2015.

Melaye however did not name the source of the allegations.

This is not the first time NNPC is being accused of deeping its fingers in the cookie jar. The firm was previously implicated in allegations of fraud in an investigation in 2012 that uncovered the $6.8 billion fuel subsidy scam, one of the biggest corruption scandals in Nigeria's history.

A spokesman for NNPC said the company would study any allegations if it is formally notified.

"NNPC has not been formally communicated on the issues. If received, the NNPC will study the alleged issues and respond accordingly," the spokesman said.

Melaye's motion neither specified how much of the 5.1 trillion Naira received by NNPC allegedly came from fraudulent activities, nor did he explain how the amount of 5.1 trillion Naira was calculated.

The motion also alleged that the NNPC sent excess refined products to storage owned by private individuals, which was then sold off illegally by those owners.