Museum workers are stanging a fresh strike in protest at changes to their contracts which they say have led to extra work and shorter breaks.
Members of the Prospect union at the National Maritime Museum and Royal Observatory in Greenwich are taking to the picket lines on Saturday.
The visitor and sales assistants at the south-east London museums took action on New Year's Day, saying imposed changes will mean they work an extra three weeks a year without proper compensation, while also having shorter breaks.
Prospect negotiations officer Caroline Hemmington said: "This strike is not about stopping people from going to the museum, but to highlight how detrimental these changes have been on the staff affected.
"Members have decided to take a second day of strike action to demonstrate to management how significantly these changes are felt on a day-to-day basis.
"Prospect is working towards finding a resolution for our members, and the best way to do this is by continuing to engage in constructive discussions with management."
A museums spokesman said:
"From November 2017, Royal Museums Greenwich harmonised terms and conditions for its front-of-house staff due to a merger of the museum's visitor experience and commerce departments.
"One of the many proposals on the table was to pay net weekly hours rather than gross, which is common within UK industry and included maintaining annual salaries at existing levels.
"This increased hourly rates of pay and proved an immediate benefit to some part-time staff and those working overtime with no adverse impact on annual salaries.
"A reduction of breaks for some of the staff involved has remained at issue and, after just over a year of negotiations with the union, discussions ceased without full agreement being achieved, so the decision was taken to impose the new terms and conditions for those staff who had not yet agreed them - some 50 out of some 200 (or 280 if all operative staff are included)."
The museum is expected to remain open during the strike.