Hundreds of healthcare workers at Derriford Hospital in Plymouth are on strike for two days from 17 June over pay.
Healthcare support workers, maternity care assistants, imaging care assistants and clinical support workers at University Hospitals Plymouth NHS Trust walked out at midnight.
The workers are demanding fair pay that better reflects their important role in patient care.
Workers' union Unison said that despite their responsibilities increasing, this has not been recognised by the employer nor have they been paid properly.
According to NHS guidance, healthcare assistants on Agenda for Change salary band 2 should only be providing personal care, such as bathing and feeding patients.
Unison said that other NHS trusts have already moved healthcare assistants to the correct salary band and agreed deals on back pay.
They added that University Hospitals Plymouth NHS Trust has refused to draw up a similar agreement, despite a "collective grievance signed by hundreds of staff".
Unison South West regional secretary Kerry Baigent said: “It’s time University Hospitals Plymouth followed the lead of other trusts in the South West and paid its healthcare assistants fairly.
“Staff are not prepared to have their hard work undervalued and have been left with no choice but to take industrial action.
“Managers should do the right thing now and avoid risking needless disruption for patients.”