Revenue and Customs (HMRC) workers in the PCS union were set to strike this coming Monday.
The workers oppose the decision to allow private companies to run call handling trials at contact centres in Bathgate and Lillyhall.
HMRC handed the contracts to Teleperformance and Sitel.
HMRC workers in contact centres, customer operations and in enquiry centres are set to walk out for half an hour at 10am and again at 4.30pm.
Workers on shifts that finish after 7pm are to leave work 30 minutes early.
A work to rule and a refusal to work overtime is already underway.
A further strike is set for 31 January.