Benefits Agency (BA) employees in Haverfordwest and Pembroke Dock are on strike this week over moves to combine the BA with job centres.
The proposed new centres, called Jobcentre Plus, would mean interviews currently undertaken behind protective screens would now be conducted face-to-face.
Julie Matthews, PCS/BA Wales organiser, said the strike was over proposals to remove the screens.
The management and government should safeguard our safety, but they are refusing the need for safety screens, she said.
Instances of assault against staff have increased 12-fold since 1987, she said. The number of recorded assaults against BA staff doubled over the past year to 5,000.
The strike will take place throughout Wales and England and will last today (Wednesday) and tomorrow (Thursday).
The vast majority of the 59 employees at Haverfordwest and 40 employees at Pembroke Dock are expected to participate.
Pat Ainsworth, PCS Union West Wales area secretary, said the strike was to protect staff against people who may be abusive or violent.
She added that there would be more industrial action in the New Year. This is just a token gesture before Christmas, she said.
Vivien Hopkins, BA Director for Wales, said: Screened areas will remain in each office for dealing with those parts of our business that entail distribution of girocheques or the more sensitive aspects, such as some Social Fund transactions.
In future, people making new claims for benefit will be invited to attend for an interview with a personal adviser and this business will be conducted in a welcoming area without screens.
Personal advisers are highly trained staff who volunteer to work in this way. Moreover, where there are unscreened areas, other devices - such as panic buttons, CCTV and security guards - will be put in place.
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