Staff at the National Gallery in London are to stage a second five-day strike in a row over the privatisation of services.
It is the second strike this month by Members of the Public and Commercial Services (PCS).
The walk out, over plans to hand visitor services to a private company, will run from 22 February.
PCS general secretary, Mark Serwotka, said the gallery was "putting its well-earned worldwide reputation as risk".
The union held its first industrial action on 2 February over the gallery's proposals.
The dispute worsened when union rep Candy Udwin, who was involved in talks at the conciliation service Acas, was suspended on the eve of the strike.
According to the PCS, the National Gallery plans "to privatise almost all staff, including those who look after the paintings and help the gallery's six million annual visitors".
"They have also reneged on a promise to introduce the London living wage, meaning the institution is the only major museum or gallery in the capital that does not pay it," it said.
The PCS has handed a 40,000 name petition to the Department for Culture, Media and Sport supporting its case.
The National Gallery said change "was essential" if the gallery was to continue "to thrive as a public entity with reduced public money".
"There is no option that allows everything to stay the same", gallery director Nicholas Penny said.
"The proposed changes are necessary to enable the National Gallery to increase income in the face of a reduced grant and increasing maintenance and running costs, and to enable it to pay all staff a minimum of the London living wage.
"The PCS union leadership opposed the change and, despite five months of dialogue, we were not able to meet an agreement."