Access to several UK museums, galleries and heritage sites may be affected this week due to industrial action.
The National and National Portrait Galleries have warned some of their rooms may be closed on Thursday.
Tate Britain and Tate Modern will open as usual but access to some galleries may be limited, while Tate Liverpool's galleries will be closed completely.
More stoppages will follow on Friday as a result of walkouts planned by the Public and Commercial Services union.
Workers at the British Museum, Natural History Museum, Science Museum and Victoria and Albert Museum in London are expected to participate.