The workers reportedly intend to strike for three days beginning April 11 in protest of working conditions. Nigeria is a key exporter of crude and a member of the Organization of Petroleum Exporting Countries.
"Considering the announcement, we suspect this is a political move and doubt any supply will ever be affected," said Kyle Cooper, an energy analyst with Citigroup. "A series of strikes by oil workers last year didn't affect Nigeria's oil production because the unions ensured that essential services kept running.
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"However, it seems that is the driving force, as OPEC appears ready to increase supply again."

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Ali al-Naimi, Saudi Arabia's oil minister, reportedly said his country wants to alleviate concern about global supplies and has 1.5 million barrels of spare capacity that can be brought up to production to stem rising prices.
"There is a possibility, though, that hard-line OPEC members have convinced their brethren that the world economy is doing fine even in the face of rising oil prices," said John Kilduff, vice president of energy risk management at Fimat.
Against this backdrop, April crude was last down two cents at $56.70 a barrel after trading as high as $57.12 a barrel on the New York Mercantile Exchange. The contract had reached all-time high of $57.60 in intraday trading last Thursday, while the highest-ever closing price was Friday's $56.42.
The May contract, which begins trading as the front-month contract on Tuesday, was last off 14 cents at $57.10. It had reached a high of $58.16 a barrel last week.
"The energy markets are likely to have a big week ahead of the Easter weekend and the supply data on Wednesday could be the catalyst to pushing prices toward $60 or back down below $55," said Kevin Kerr, president of Kerr Trading International.
For his part, Mr. Kerr predicted short covering early in the week would propel prices to an all- time high. He also expects to see increases in crude and heating oil supplies and a contraction in gasoline inventories when the Energy Department and the American Petroleum Institute issue their respective weekly supply data updates on Wednesday.
"The 'hysterical blindness,' which the vast majority of traders are falling into, simply has caused this market to run too high, too fast and a correction may be due," Mr. Kerr said.
Mr. Cooper is looking for a buildup in weekly U.S. crude stocks, along with a slight decline in gasoline supplies and a decrease in distillate supplies, though at a rate less than what had been reported last week.
April gasoline ticked up 1.25 cents at $1.588 a gallon, after rising 3.8% last week to close at a record high of $1.5755. The average price of gasoline in the U.S. rose to a record level in the past two weeks and is expected to climb even higher, according to a survey released Sunday.
According to the AAA Daily Fuel Gauge Report, the average price for a gallon of regular unleaded gasoline in the U.S. is $2.072.
April heating oil advanced 0.12 cent to $1.573 a gallon.
Meanwhile, natural gas slipped 3.3 cents to $7.24 million British thermal units after surging 7.4% in the latest week.
"With the end of winter in sight and abundant inventories, most think it's a sale but nobody is willing to test buyers' resolve," Mr. Kilduff said. "Clearly, a major issue is going to be the prevailing level of crude ... which actually poses a much larger bearish risk from current levels."
Mr. Cooper said he expects the Energy Department to report a natural-gas storage decline similar to the 95 billion cubic feet reported last week. Last year, the drawdown in gas inventories was 65 billion cubic feet.
Oil and gas stocks fell in morning trading, and the Amex Oil Index last stood at 864.26 points, down 1.2%.