Union members at the site will walk out on Friday after rejecting an offer.
The dispute involves employees of Balfour Beatty Engineering Services Limited (BBESL), Petrofac, and BIS.
The row is over a claim for an additional £50 a day to compensate for complaints that suitable accommodation is not available, and lengthy travelling times for employees.
Phil Whitehurst, national officer of the GMB union said "At a mass meeting this afternoon, members have voted unanimously to reject the management's final offer, which carried the officers' recommendation to accept.
"Management have now taken it off the table and members will strike on Friday."
The new facility is being built to process gas and liquid hydrocarbon reserves on a site to the east of the established Sullom Voe oil terminal on Shetland.