A group of oil service workers in Norway said on Monday they will go on strike as wage talks broke down, while a second labour union said it had reached agreement with the industry and would continue working.
There was no immediate expectation that oil and gas output would be affected.
The Safe labour union said 154 of its members immediately began a strike and will be followed by another 224 workers from June 18 unless a bargain is struck by then.
The companies initially affected were SLB SLB.N, DOF Subsea, Halliburton HAL.N, Weatherford, Tios and DeepOcean.
The larger Styrke labour union said it had reached a deal and would not take strike action.
A government-appointed mediator separately confirmed that negotiations between Safe and the industry had been unsuccessful.
"We are disappointed that no agreement was reached with Safe," industry group Offshore Norway said in a statement.
Overall, the wages talks covered some 6,000 members of Styrke and about 1,800 members of Safe.
(Reuters - Reporting by Terje Solsvik, editing by Nerijus Adomaitis)