On Tuesday, hundreds of staff at London's National Gallery began an indefinite strike.
SIA reports quoting the local media that the latest in a series of walkouts to protest at the outsourcing of some services to the private sector.
Members of the Public and Commercial Services (PCS) union have staged 56 days of action since February after plans were revealed for privatising certain services, which the gallery said would allow it to "operate more flexibly and deliver an enhanced service".
The museum is London's second most popular tourist attraction, drawing around six million visitors per year.
It will stay open during the latest strike, although some rooms will be closed and many educational workshops have been cancelled.