Twelve Lerwick Port Authority (LPA) workers will walk out on Monday, after they rejected an updated pay offer from the LPA.
Barring a last-minute intervention from the port authority over the weekend, the dozen shore workers will down tools from 12:01am on Monday.
Union Unite said their members received a new pay offer on Wednesday afternoon, which was “unanimously rejected”.
Industrial officer John Clark said the workers and the LPA are a “long way off” with regards to two key issues – overtime and the group’s work-life balance.
Mr Clark said the LPA’s latest offer was “simply not good enough”.
“The strike will be going ahead on Monday, unless something happens over the weekend.
“My members are completely unhappy. They are historically underpaid, and this offer greatly reduces their earnings.”