About 500 workers of the National Heritage, the state body charged with looking after Spain’s palaces and other historical sites, will strike on Holy Thursday on March 28 and Good Friday on March 29, the CSI-F union said.
Among the sites affected will be Madrid’s vast Royal Palace, built on a high bluff overlooking the Manzanares river and which is used for state occasions; the Valley of the Fallen mausoleum, where dictator Francisco Franco is buried; and the Escorial Palace near Madrid.
While most National Heritage workers are employed at tourist sites, some are employed at the Zarzuela Palace outside Madrid, where King Juan Carlos lives with his wife Sofia.
The strike would not affect the royal family, a spokesman for the royal household said.
The union said the sites could lose some 100,000 visitors because of the strike.
National Heritage staff say they are furious over government measures that have slashed their wages by 15 percent and extended their working hours.
The first strike by palace workers comes at a delicate time for the king, who is recovering in hospital after undergoing lower back surgery over the weekend while his son-in-law Inaki Urdangarin is under investigation for allegedly embezzling millions of euros of public money.