Offshore workers have rejected the latest offer in a long-running dispute over pay and conditions.
Members of the Unite and GMB unions voted against a second offer by the Offshore Contractors Association (OCA).
Unite regional officer Tommy Campbell said: "We have repeatedly warned the OCA employers and other offshore employers that we cannot simply have a race to the bottom, with companies competing with each other to suppress the pay and conditions of offshore workers.
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"It's bad for our members and it's bad for the local economies that rely on their incomes.
"Those companies who invest in their workers and see them as genuine partners will reap the benefits in the future. Those who don't will end up lagging behind, and will always face the possibility of industrial action from their workforce.
"We will now consult with our union members and Unite workplace representatives about the way forward, given they now have a mandate for an industrial action ballot following the rejection of the pay offer."
Unite is seeking a significant wage increase for members, along with improved sick pay and paid travel time to an employer's onshore base.
Dave Hulse, national officer of the GMB, said: "This result comes as little surprise given the attacks our members have faced on their pay, terms and conditions in recent years. The offer the employers have made is just not up to scratch.
"Our members believe that over recent times they have been treated with contempt."