Members of the Rail, Maritime and Transport (RMT) union and Unite, employed by the Wood Group on Shell platforms, walked out at 6.30am on Tuesday, with further stoppages planned in the coming weeks.
Around 400 workers are involved in the strike, as well as a ban on overtime, following overwhelming support for action from members of both unions.
Officials say workers’ pay and allowances could be cut by as much as 30% following the downturn in the industry.
RMT general secretary Mick Cash said: “After savage redundancies and attacks on workload and working conditions, this group of offshore workers are now told that they are going to be railroaded into accepting pay cuts of up to 30%.
“We are well aware that the company chief executive has had a pay increase of 28% to bring him up to £600,000. It is obscene that while the top bosses are lining their own pockets they are kicking the workforce from pillar to post.
“This brave group of workers are taking a stand against the greed and savagery that is a mark of corporate Britain in 2016. They deserve the full support of the entire trade union movement.”
Unite regional officer John Boland said the dispute was the first in the North Sea for three decades and its members felt “backed into a corner”.
He said: “To say we are disappointed it has had to come to this is an understatement, but bosses at Wood Group are simply not listening.
“Our members have been faced with changes to shift patterns which have seen them working longer offshore for the same pay and as well as having three rounds of redundancies imposed on them. This attack on their pay and allowances has pushed our members too far this time.
“For decades, oil and gas companies across the North Sea have made hay while the sun shone and become very profitable on the back of the hard work and dedication of our members. Now the weather has turned for the industry, they are using the downturn to attack the pay, terms and conditions of our members.”
Dave Stewart, chief executive of Wood Group’s eastern region business unit, said: “Our employees’ safety and well-being remains our top priority and our commitment is to ensuring it is not compromised during industrial action. Although we are extremely disappointed that industrial action will be taken, we respect the right of those employees who choose to do so.
“Our firm focus remains on reaching a resolution, which meets our mutual goal of sustaining these jobs for our employees in the North Sea now and in the future, against the backdrop of an extremely challenging climate created by the sustained low oil price.
“We are continuing to engage frequently, proactively and openly with our employees and the unions. We met with union representatives on Friday and senior management have visited impacted installations over the weekend to talk with our people, with the clear aim of positively progressing discussions towards reaching a resolution.”