Thousands of workers in Jobcentre Plus call centres are staging a 48-hour strike in a row over working conditions and claims of "excessive monitoring".
Members of the Public and Commercial Services union (PCS) at seven sites - Glasgow, Newport in south Wales, Norwich, Sheffield, Makerfield, near Wigan, Bristol and Manchester, are taking part in the industrial action after previously voting in favour of a walkout. Up to 3,500 workers were expected to take part.
The union said staff have complained about "intolerable" conditions, including excessive monitoring and inflexible working conditions.
The PCS claimed that the perceived drop in the number of people receiving Jobseeker's Allowance despite a big increase in unemployment confirmed its fears that a backlog of claims was mounting up.
About 10 PCS union representatives stood outside the Jobcentre Plus call centre in Atlas Road in Springburn, Glasgow, on Thursday. Officials estimated that 325 of the 340 staff at the centre had not turned up for work.
The union has said it wants staff to have the same flexitime arrangements as in the rest of the Department for Work and Pensions, more varied, satisfying work and an end to a "target" driven culture, particularly by changing the way "unrealistic average call times" are used.
Officials claimed "oppressive" working conditions in Jobcentre Plus were causing high levels of stress and sickness, adding that staff were leaving at an "alarming" rate.
Speaking on the picket line, David Coventry, who has worked at the Jobcentre Plus building for six years and the Department for Work and Pensions for 20 years, said 30 to 35 employees had been off work at some point with work-related stress in the last year as a result of the "micro-management".
He said: "This is actually unusual, in a sense. Whilst it's always a last resort to take industrial action, staff are actually at the end of their tether now because even if they currently have not had a sick absence through stress, everyone is under stress to a greater degree because of the constant pressure of being micro-managed."
A DWP spokesman said: "We are disappointed that some staff - only 21% across the centres - have voted to take industrial action. No jobs will be at risk through these changes. The contact centre staff at DWP will continue to receive good terms of employment, including generous holidays."