Nigeria's main trade union body is planning a second general strike over fuel price rises, and has warned it will target oil exports.
Leaders of the Nigeria Labour Congress have branded oil giant Shell an "enemy of the Nigerian people" and called for action against the Anglo-Dutch firm.
Shell has tried to bar two unions from striking, blaming internal issues.
The threat of a industrial action sent crude prices higher as Shell accounts for about half of Nigerian oil exports.
The firm is not the source of the price rises, which stem from the Nigerian government's cuts to fuel subsidies.
But NLC leaders now seem to see disrupting oil production as the best way to increase pressure on President Olusegun Obasanjo's government after a four day national stoppage in October failed to reverse the price rises.
NLC president Adams Oshiomhole said that the next strike - due to start on 16 November - would be indefinite and total, hitting both the production and export of crude oil.
"Last time there was no disruption of the upstream oil sector. Now the only way for the government to listen is to interrupt the oil flow," he said.
The price of US light, sweet crude oil, used by the oil industry as a benchmark, rose more than 50 cents in Asian trade on Monday, topping $52.25. It fell back from that high and by early afternoon in New York was trading below $50 for the first time since October.
"Shell has decided to side with the government to oppress our people and to mix themselves into Nigerian internal politics," said Mr Oshiomhole.
He accused Shell of taking legal action to prevent a white-collar oil union from joining the strike.
A Shell spokesman in London said the firm was seeking a restraining order to stop two local unions from striking, but that this was unrelated to the planned NLC action.
Shell said its court case was brought about because two in-house unions walked out on an earlier occasion, contravening a collective agreement, the spokesman said.
The judge adjourned the case until 18 November, two days after the start of the planned general strike, Agence France Presse reported.
The issue of fuel subsidies has become the major battleground between the NLC and the government.
The NLC has dismissed government measures to help alleviate the impact of the increased fuel costs, saying they fell short of its demand for a drop in petrol prices.
Any block to Nigerian oil exports may inflate already high global prices.
The NLC's last general strike over the fuel price rises ran from 11 October to 14 October, shutting down banks, businesses, shops and public services, but did not hit oil exports.
Nigeria is the world's seventh biggest oil producer, and America's fifth most important supplier, making the country's ongoing labour unrest a cause for concern in the oil sector.
The government "is showing pointed ingratitude to the men and women who have... toiled not just to relieve the pains in the land, but also to reduce the high tension in the country," the NLC said in a statement.
On Friday the Nigerian government introduced a number of grants and tax reductions to help offset the recent 23% rise in fuel prices.
Global oil prices have increased by 60% since the beginning of 2004 due to a combination of rising demand and worries over supply.