Chevron had no immediate comment, while Exxon Mobil had not responded to a request for information
Oil firms operating in Nigeria have sacked about 3,000 workers, a labour union official said on Wednesday, calling on the government to file a protest with foreign oil operators.
"The government should call the multinationals to order. They are sacking and closing shop," Igwe Achese, president of the National Union of Petroleum and Natural Gas, told Reuters after a union meeting.
"So we want government to act. That's why we have given a 21-day ultimatum," he said. "We believe government would act. If they don't, when we get to the bridge, that is at the expiration of the ultimatum, we will cross it. I don't want to use the word 'strike' now."
Nigeria's Premium Times said on its website that Exxon Mobil, Chevron, Pan Ocean and Saipem were among the firms that had dismissed oil workers.
Chevron had no immediate comment, while the Premium Times said Exxon Mobil had not responded to a request for information.
The oil industry has been hit by low crude prices and a wave of militant attacks in Nigeria's oil hub, the Niger Delta. Several foreign firms have evacuated expatriate staff from the southern region due to the violence or scaled back activities.
Nigeria pumps around 1.9 million barrels a day, the Oil Ministry said in a tweet on Monday. That is less than the 2.2 million bpd at the start of the year but better than the 1 million bpd reported a few months ago because of militant attacks.