Workers across the Department for Transport are taking rolling sectional strikes until 3 August.
The PCS action is a continuation of a month of strikes in June, and has so far seen strikes by DVLA driving instructors and coastguards in July. Further strikes are set to take place at the DVLA on the 27 July and 3 August.
The 8,000 workers in the department are fighting an onslaught on terms and conditions, job cuts and office closures. They are demanding decent pay and for staff to retain their civil service status.
A strike would see 6,000 workers across 32 call centres taking action. The group executive committee meets this week to decide on the next steps.