Members of the PCS union who work for contractor Balfour Beatty at the Department for Work and Pensions (DWP) walked out for two hours on Tuesday of this week.
The strikers work in call centres, job centres and offices at locations including Glasgow, Watford, Cardiff, Washington, Fylde and London.
They are angry that around 300 colleagues are facing compulsory redundancy on the lowest terms allowed by law.
Around 700 PCS members work for Balfour Beatty to provide the DWP with services such as messengers, typists and telephone staff.
In a ballot 59 percent of those taking part voted for strike action, while 80 percent voted for action short of a strike. The walkout, which started at 9.30am, will be followed by action short of a strike.