Museum workers start an eight-week strike on Saturday in a dispute over pay.
More than 200 members of the Public and Commercial Services union (PCS) at National Museums Liverpool (NML) will take industrial action.
The union said it had offered to have a £1,500 payment it says is due paid in two instalments but it was turned down.
The NML is the only one of more than 200 employers not to have honoured the £1,500 payment which helped resolve a national dispute last year, said the union.
PCS general secretary Fran Heathcote said: “PCS has tried our hardest to resolve this dispute, but we have been met with a straight ‘No’ from the employer.
“Our fight is not with those people who visit the museums – it’s with those who undervalue our members’ passion, skill and knowledge at work.
“It’s time for NML to pay up and recognise the contribution our members make to the economic and cultural wellbeing of Liverpool.”
The strike action will run from Saturday to April 14 and is likely to affect four museums (the Museum of Liverpool, the World Museum, the International Slavery Museum and the Maritime Museum), as well as the Walker Art Gallery, Sudley House and the Lady Lever Art Gallery, said the union.