PCS union members in Wales struck for the third time last weekend over pay and pensions.
The walkout affected six National Museum of Wales sites last weekend.
Workers are angry at attacks on allowances for weekend and bank holiday working.
The cuts will impact on the value of their pensions.
The action hit the National Museum in Cardiff, St Fagans National History Museum, the National Waterfront Museum, Big Pit National Coal Museum, the National Slate Museum and the National Wool Museum.
Some 92 percent voted for strikes in a ballot, on a 57 percent turnout.