More than 150 porters, domestics, catering and security staff will walk out on 12, 15 and 16 of September - with more dates set to follow.

The workers believe they get worse terms and conditions than colleagues working at the same hospital. The staff have been outsourced to AGH Solutions (AGHS), a wholly owned subsidiary of Airedale NHS Foundation Trust.

The GMB claims AGHS uses its subsidiary status to not honour the NHS Agenda for Change terms and conditions, including NHS pensions, sick pay rates, annual leave and Sunday working enhancements.

Joe Wheatley, GMB organiser, said: ‘The trust claims to value dignity and inclusion yet allows AGHS to treat its workers as second-class citizens. It's time to match words with action and give NHS pay for NHS jobs.

‘GMB is calling for urgent talks with AGHS and the trust to resolve the dispute.'

In response, Dennis Kentrop, managing director at AGHS, said: 'Although some of our staff are on different terms and conditions as a result of their protection under TUPE regulations, we value every member of the team equally. We offer very competitive AGHS pay, terms and conditions which continue to attract talented individuals to the company and provide valuable opportunities for local employment.

'We remain committed to continually improving AGH Solutions Limited as a place to work and, following recent negotiations with GMB, we further improved upon our proposal.

'I hope that we can continue to work with the GMB to resolve this before 12 September. However, should industrial action take place, we have contingency plans in place to maintain the services that we provide to Airedale NHS Foundation Trust.'