Healthcare assistants have staged a protest over concerns they are underpaid for their work.
The workers, who are members of the union Unison, took part in the protest outside James Cook Hospital in Middlesbrough on Thursday 23 November.
Clare Williams, Northern regional secretary for Unison, warned further action could be taken, including strikes.
The dispute is over whether healthcare assistants have been banded appropriately.
South Tees Hospitals NHS Foundation Trust said it had already agreed to move some staff to a higher grade.
However, Unison said the current offer was not adequate.
Ms Williams said: “It is time South Tees NHS Trust followed others’ lead and paid their healthcare assistants fairly.
“Staff are not prepared to have their hard work undervalued. If the trust continues to refuse to pay them properly then the health workers will be left with little option but to consider strike action.
“Managers should do the right thing and avoid risking needless disruption for patients.”
Unison claims support staff are routinely undertaking clinical tasks, such as taking and monitoring blood, performing electrocardiogram tests and inserting cannulas.
The union said they were being paid a band two salary but should be on band three - which amounts to £2,000 more a year - due to the work they are carrying out. They are asking for the workers to be moved to the higher grade and be back-paid to 2019, depending on how long they have worked at the hospital.
The union added other NHS trusts are moving healthcare assistants to the correct salary band and providing appropriate back pay.
Rachael Metcalf, South Tees Hospitals NHS Foundation Trust’s director of human resources, said: "We recognise and appreciate the huge contribution that healthcare assistants make to our patients.
"Since national changes to the NHS salary band for these important and valued roles, we have been working closely with our local trades union colleagues and have accepted in full their proposal to move relevant colleagues to a higher grade, including back-pay arrangements where these apply."
Responding, Ms Williams said: "The trust sadly have not negotiated with Unison. We have asked to meet them on more than one occasion. We asked them to come today.
"We've got hundreds of healthcare assistants who have signed grievances and are very determined to ask the trust to value them and to recognise their invaluable role - to come and meet with Unison and negotiate an agreed settlement to this issue."
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