Thousands of public sector workers in British courts, job centres and museums went on strike for better pay on Wednesday, prompting an angry response from the government.
The Public and Commercial Services union said around 250,000 of its members would take part in the strike but the government said only 80,000 would join industrial action.
Striking workers protested outside the High Court in London and the National Gallery, where most rooms were closed except for the Rembrandt exhibition, which opened to the public for a four-month run on Wednesday.
PCS leader Mark Serwotka said that pay cuts "have slashed living standards of public servants and their families".
The move comes after employees in the National Health Service (NHS) went on the strike for the first time since former prime minister Margaret Thatcher's era and ahead of a planned major demonstration in London on Saturday by government opponents.
The government accused the union of being "irresponsible" because it was pressing ahead with the strike even though a minority of public sector workers backed it.