Unofficial protest held on North Sea oil rig
They downed tools at Statoil's Mariner platform, 95 miles east of Shetland.
Scores of employees for contractor Aker Solutions are said to have stopped work in the four-hour sit in, alleging poor working conditions.
There is no union involvement in the action. James Furie, a spokesman for the workers, claimed up to 200 Aker Solutions employees are involved.
He said: ''Today brings a day of unofficial action against working conditions on the Mariner hook up,'' he said.
The workers are protesting against poor working conditions, poor management, possible blacklisting and having an offer of a bonus removed.
This action will escalate if Aker and Statoil think they can continue to treat us this way.''
An Aker Solutions spokesman said: ''Aker Solutions has been made aware that some workers based at the Mariner field have chosen not to work today.
The company has received no official notification of this activity and is looking into this matter.''
The company is understood to employ more than 500 workers on the platform.