President Umaru Yar'Adua has ordered Nigeria's state-run oil company to demand nearly $2bn in arrears from two major oil companies.
The government say Royal Dutch Shell and ExxonMobil have not paid taxes and production sharing costs they owe on two offshore oil fields.
The companies say they have followed the law and are in discussions with the government.
Militant attacks and funding troubles have seen Nigeria cut its production.
"ExxonMobil affiliate fully complies with all laws and regulations and has paid taxes and royalties to Nigeria accordingly," ExxonMobil said in response, AFP reported.
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Ofgem fines National Grid Ј41.6m ... routinely has ongoing discussions with a number of government agencies on a variety of topics, including tax. We do not comment on ongoing discussions," it said.
Shell Nigeria Exploration and Production Company (Snepco) refused to comment while there were "ongoing discussions" between it and the government.
The Production Sharing Contracts agreed with the oil majors in the deep water production fields are coming up for renegotiation.
A BBC correspondent says the price of oil has rocketed since they were first negotiated and the government may be trying to improve their negotiation position.
At the same time, the Nigerian National Petroleum Company (NNPC) has not been able to fund its share of the joint venture agreements for on-shore oil production, and is trying to find other ways of paying for them, says the BBC's Alex Last in Lagos.
Militant attacks and strikes by Nigerian oil workers have helped push oil prices to record highs.
(BBC)
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