Members of the Public and Commercial Services union (PCS) working for the National Museum of Science and Industry (NMSI) are furious that a below inflation pay offer has been imposed on them at a successful time for the museum.

Over 85% of PCS members taking part voted to strike and over 70% voted for industrial action short of a strike. Their colleagues who are members of Prospect also strongly backed industrial action in their ballot.

NMSI, which includes the Science Museum in London, also operates a trading company to generate income, and made an operating profit of over £1 million last year, exceeding its target by over 14%. Staff in the trading company are on worse terms and conditions than museum staff, including having no access to civil service pensions.

NMSI chief executive Martin Earwicker has proposed sweeping changes, including applying trading company terms and conditions to new museum staff, and has not ruled out charging visitors. The Department for Culture, Media and Sport permanent secretary, Jonathan Stephens, and minister of state, Margaret Hodge, have refused to meet union representatives to discuss the plans.

Other museums affected are the National Museum of Photography, Film and Television in Bradford, the National Railway Museum in York, and the Science Museum Swindon in Wiltshire.

Ragesh Khakhria, PCS negotiations officer, said: “These proposals have serious implications, not just for staff but for the long term future of our museums. At the very least members expect to be consulted, and they certainly should be involved in any changes to their pay and working conditions. ”

PCS general secretary Mark Serwotka added: “This overwhelming strike vote should serve as a wake up call to museum management and the government that our members regard their short-sighted proposals as an unacceptable attack on their livelihoods and the public service ethos of these respected institutions.

“If it is to avoid a damaging dispute, the museum needs to recognise the anger and frustration this is causing among staff and sit down to agree a fair and reasonable way forward.”