Fuel prices in Nigeria more than doubled a day after the oil-rich nation ended a popular consumer fuel subsidy.
Prices at the pump on Monday soared from about 40 cents to 88 cents per liter.
Witnesses reported that police in the capital, Abuja, used tear gas to disperse dozens of people who had gathered to protest the new fuel rates.
The Nigeria Labor Congress and the Trade Union Congress said that in coming days they will call for nationwide strikes and mass protests. The unions said in a joint statement that the subsidy elimination is "callous and insensitive."
The fuel subsidy was one of the few benefits of Nigeria's oil wealth enjoyed by the average person.
Nigerian President Goodluck Jonathan has said the money used on the $7.5 billion subsidy program would be better spent on infrastructure and social programs.
Nigeria produces more than two million barrels of crude oil a day. But it must import refined fuel because Nigeria's refineries lack proper infrastructure and management.
Militants in oil-rich southern Nigeria attacked government and oil industry targets for years, demanding that more oil revenue be spent on impoverished communities in the region.
The attacks largely stopped after a government amnesty in 2009, but oil firms still battle tapping and sabotage of their pipelines.
Some lawmakers in the House of Representatives have said they will fight to bring back the fuel subsidy.
Some information for this report was provided by AP, AFP and Reuters.