Nigeria's main oil workers union threatened to join a nationwide strike and shut down the country's oil industry as a court rejected a government attempt Wednesday to halt the work stoppage.

The strike, launched Monday, has closed most major businesses, but has not yet disrupted Nigeria's daily export of 2.5 million barrels of oil. Still, the union's move Wednesday fed concerns about global supply that have helped send prices to record highs.

The union, NUPENG, said its members were manning key positions for now, but vowed to turn off the spigots if the government used heavy-handed tactics to end the protest.

"If there are arrests, we will change our strategy. . . . We can move to stop operations 100 percent," said the union's president, Peter Akpatason.

"We're still allowing critical aspects of production and export operations to go on," but the union was not letting fresh crews replace those now at work, he said.

Nigeria, a nation of more than 130 million, is the world's seventh-largest oil exporter and the fifth-largest supplier of oil to the United States.

Nigeria's leading labor union, the Nigeria Labor Congress, has threatened to extend the strike beyond Thursday. It was supposed to last four days and resume again in two weeks if the government failed to lower local fuel prices.