Cabinet Office minister Francis Maude has called the PCS' decision to strike "futile, counter-productive and irresponsible."
He added that the decision to strike benefits no one, but "threatens the services people rely on."
He said: "I can reassure the public that the Government has done everything we can to minimise disruption [today]. Rigorous contingency planning is in place to try and limit the impact of the strike action and to ensure that affected public services operate as effectively as possible."
More top news
A dry and fine weekend for most, with scattered showers and heavier downpours in Scotland.
Floods are an annual occurrence in parts of India during the monsoon season, which runs from June to September.
Crew members of the IchorCoal paid tribute to two sailors who died during the 11-month circumnavigation of the globe.