Staff in the Science Museum, London, the National Railway Museum, York, the National Media Museum, Bradford, and the Science Museum in Swindon - which collectively make up the National Museum of Science and Industry – are being asked to vote for a series of one-day strikes along with a campaign of action short of a strike.

The move is a reflection of the frustration felt by members who have effectively endured a pay freeze during the eleven months since the due date of their salary increase. They are still waiting for a formal pay offer.

Prospect has refuted the museum’s claim that uncertainty over the outcome of the last comprehensive spending review prevented it from submitting its pay remit to the government earlier. Instead, the union claims the principal reason for the delay was the magnitude of fundamental changes to the pay and terms and conditions of staff, originally included as part of the pay negotiations.

Prospect negotiator Emily Boase said: "Although we have yet to receive a formal offer, NMSI management have made it clear that they are seeking to lower the average and maximum pay rates for the job, abandon previous commitments to introduce pay progression into the pay system and close the pension scheme to new entrants.

"Not only would this leave many of the most experienced staff without any pay increase for years to come, but plans to increase the element of performance-related pay will do little to improve retention among specialist roles where accumulative knowledge is vital to the interpretation of the collection.

"The impact of these proposals would be huge yet management’s decision not to submit its pay remit until seven months after its April due date left little time for meaningful consultation and the suspicion that NMSI never intended to enter into genuine talks."

The changes to the terms and conditions are part of a wider programme of reform backed by NMSI’s director Martin Earwicker which includes shedding the museum’s status as a non-departmental public body – a move in-line with the museum’s current commercially reliant strategy, but one the union fears could lead to the re-introduction of admission charges.

The ballot closes on 18 February with the results available soon afterwards. NMSI warders, security and administrative staff represented by the PCS union are also being balloted on strike action during the same period.