Nearly 20,000 civil servants are to hold a 24-hour strike in a long-running dispute over pay.
Pay and working conditions are sticking points, unions say
The Public and Commercial Services Union said members at the Ministry of Defence and the Identity and Passport Service will walk out on 30 March.
At the same time workers at another four departments including Health and the Crown Prosecution Service will begin a month-long work to rule.
Workers at every other Whitehall department will join them for a day.
The union says it is taking action over pay rises this year which, it says, have been below the rate of inflation.
A spokesman said MoD staff have been offered a 2.5 per cent pay rise.
According to the Consumer Prices Index (CPI), inflation in February was 2.8% while the Retail Prices Index (RPI) was at 4.6%.
The union is also in dispute over jobs and working conditions for its members.
Workers in the Crown Prosecution Service, Department of Health, Land Registry and Learning Skills Council will work to rule for a month, also over below inflation pay offers.
A union spokesman said this meant they would work exactly to the terms of their contract.
They will not do any paid or unpaid overtime, and take all the lunch and rest breaks they are entitled to.
They will be joined by up to 230,000 PCS members in all other Whitehall departments on 30 March for 24-hours.