North Sea oil rig workers struck for 12 hours on Monday and a 24-hour strike is planned for Monday 20 August.
The three platforms affected are Alwyn, Dunbar and Elgin.
The workers are members of the Unite union and are striking against changes to their rotas that would see them working three weeks on and three off.
That’s compared to the two weeks on and two off shift pattern they work at the moment.
The employer is the Total energy firm.
Workers at Total’s Shetland gas plant have voted to accept a deal on pay by 65 percent on a 94 percent turnout.
They voted on Friday to accept the improved pay offer after having voted for strikes in June.
The new deal leaves workers’ shift patterns unchanged.
They work three weeks on and three off.
The Unite union said it had secured from bosses “a commitment not to negatively change the rota for the next three years”.
GMB and Unite union members on the Equinor Mariner oil rig have voted to accept an improved deal over pay, terms and conditions.
Some 75 percent of GMB union members and 68 percent of Unite union members voted for the new deal.