Striking hospital theatre staff have walked out in a dispute over pay and job banding.
Their union, Unison, said the workers carry out Band 3-level clinical duties in operating theatres, but are only paid Band 2 salaries.
The action is affecting sites run by the Leeds Teaching Hospitals NHS Trust.
Dr Magnus Harrison, the trust's chief medical officer, said it was "working closely with theatre colleagues to minimise disruption to patients during the periods of strike action".
Michelle Ellse, a Band 2 perioperative assistant, said staff were doing complex clinical work while being paid close to minimum wage.
"We get emergency blood when it's needed, we weigh swabs to check blood loss and we monitor it with the team. We speak to the surgeon and the anaesthetist about the fluids and the blood loss.
"We look after visitors, medical students, X-ray attendants, and ensure the environment remains sterile, whilst carrying out clinical tasks.
"People outside theatres don't see that."
Ellse said staff felt they had been left behind compared with colleagues in other parts of the country.
"As staff, the morale has fallen, we're going above and beyond without being paid for the work we're doing, people are stressed and anxious. We don't want to strike, we just want to be paid fairly," she said.
"We are not asking for anything extra. We just want to be paid for the job we already do," she added.
The walkout is the third in the dispute and will run for five days across Leeds General Infirmary, St James's Hospital and Chapel Allerton Hospital, according to Unison.
The union said theatre assistants were on Band 2 but carried out duties that matched the national profile for Band 3 roles, including setting out sterile equipment, operating machinery and supporting patient safety in operating theatres.
Imogen Woods, Unison's Yorkshire and Humberside area organiser, said the trust had not put an offer on the table.
"These workers care about patients and they are paid 15p above minimum wage to do a complex job. The trust can get round the table at any time," she said.
"Staff have been raising concerns for more than a year; they have been patient and reasonable. They are simply asking to be treated the same as workers in other trusts," she added.
Unison said that more than 100 NHS trusts and health boards in England and Wales had already agreed similar re-banding and back pay deals since 2021.
Woods also said that the trust's chief executive, Brendan Brown, had resolved a similar issue whilst in his previous post at the Calderdale and Huddersfield NHS Foundation Trust.
Harrison added: "We remain committed to ensuring all colleagues feel valued and able to raise their concerns."