The Science Museum is to close today as staff strike over a pay deal they have described as "derisory".
Hundreds of curators, conservators, managers and other employees at London's Science Museum, the National Railway Museum in York and the National Museum of Photography, Film and Television in Bradford will take part.
The strike has been timed to coincide with schools' half term holidays for maximum impact.
Staff claim a 2.5% pay offer is below inflation.
Catherine Craig, negotiations officer for the Public and Commercial Service union, said: "Faced with a pay offer that fails to implement previously agreed improvements and what amounts to a real-terms pay cut for many, our members are left with no option but to strike."
Management blames lack of funding and free admission, which has led to the closure of some of the galleries.