Nigeria's main oil union has said it will shut down the country's oil and gas production from Sunday, as part of a national strike over a massive spike in petrol prices blamed on the government.
"We are herby notifying the Federal Government of Nigeria ... that PENGASSAN (The Petroleum and Natural Gas Senior Staff Association of Nigeria) shall be forced to go ahead and apply the bitter option of ordering the systematic shutting down of oil and gas production with effect from ... 00:00 hours on Sunday Jan 15," the union said in a statement.
Later on Thursday, Nigerian President Goodluck Jonathan entered a meeting with labour unions, in an effort to end a strike.
A Reuters reporter saw a group of nine representatives of the main labour unions.
The protests in Africa's largest crude producer have put the government under mounting pressure as a nationwide strike entered its fourth day on Thursday.
Hundreds of thousands of people have staged protests in cities across the country, demonstrating against the January 1 removal of fuel subsidies that doubled the price of petrol overnight.
Many of the protesters see the the government's withdrawal of financial support as another blow to the the public's needs by not tackling the rampant corruption that has severely damaged the country's economy.
Nigeria exports about two million barrels per day and is a key supplier of crude to the US and the European Union.
An official with one of Nigeria's main trade unions said they would not negotiate with President Goodluck Jonathan's administration until it reinstated fuel subsidies, which many people view as their only benefit from the nation's oil wealth.
"For us to negotiate, the price of fuel must revert to 65 naira," said Denja Yaqub, secretary general of the Nigerian Labour Congress.
Members of Nigeria's senate and house of representatives have sought to broker a way out of the crisis, but no progress has been reported so far.
Another meeting was set for later Thursday.
In northern Nigeria's largest city of Kano, several hundreds of thousands of people gathered at an expansive open air ground for what organisers labelled a "sit-in" rally.
In Lagos, a city of 15 million, a crowd of more than 10,000 packed a park which has become the main protest site in the economic capital.
Some watched from atop a bridge, as a truck of protesters drove by the crowd chanting "Ole! Ole!" (thief in the local Yoruba language).
"We have gathered here for a sit-in strike and will not leave until the fuel subsidy is restored," Isa Yunusa Danguguwa, a union leader in Kano said.
Dele Olaniyi, a 54-year-old taxi driver Dele, vowed to stay put until the government backs down.
"I have been taking part in the protests since Monday and will continue until the government goes back to 65 naira ($0.40) a litre," he said.
"The majority of our people are too poor to afford the new price."
Government officials and economists say removing subsidies was essential and will allow the $8bn per year in savings to be plowed into projects to improve the country's woefully inadequate infrastructure.