Up to 270,000 civil servants have begun a 48-hour strike against cuts to redundancy terms.
The Public and Commercial Services Union (PCS) organised the walkout in response to changes to the civil service compensation scheme, which it says will lead to staff losing a third of their entitlements.
Courts, jobcentres, driving tests, tax offices, border controls and passports, together with civilian staff working for the Metropolitan police and parliamentary security staff, are among the services affected.
"The government is tearing up the contracts of low paid civil and public servants whilst it claims it can do nothing about bankers' bonuses because of contractual obligations," PCS general secretary Mark Serwotka said.
"The government need to recognise that slashing entitlements and cutting jobs on the cheap will damage public services and reach an agreement that protects existing members' entitlements."
Cabinet Office minister Tessa Jowell said the government was confident the public would be able to access public services despite the strike. She said less than a fifth of PCS members had backed industrial action - no more than ten per cent of all civil servants.
"The changes to the civil service compensation scheme were agreed with five of the six civil service unions after 18 months of negotiation and consultation," she said.
"These unions all agree with us that the resulting deal is fair for staff and taxpayers."
Ministers argue the package brings the civil service more into line with the rest of the public sector.
But the PCS strike continues nonetheless. Picket lines across London will be toured by a 'battle bus' as government departments in Whitehall, parliament and the Royal Courts of Justice are visited tomorrow. A march is also taking place in central London on Tuesday lunchtime.