Unison says staff at eight hospitals in the area - Morriston, Singleton, Neath Port Talbot, Cefn Coed, Gorseinon, Cimla, Tonna and Glanrhyd - will walk out on 10 and 11 December.

The action follows a ballot that saw 99% of workers who took part voting in favour of a strike.

Healthcare support workers on salary band 2 should only be providing personal care such as bathing and feeding patients, according to NHS guidance.

However, Unison claims healthcare assistants employed by the Swansea Bay University Health Board are routinely undertaking clinical tasks such as monitoring blood, performing electrocardiogram tests and inserting cannulas.

Unison Cymru regional organiser Lianne Owen said: ‘Strike action is always a last resort, but board managers must come back with an offer that compensates staff fairly for all the time they've been paid incorrectly.

 ‘Healthcare support workers are some of the lowest paid staff in the NHS. Yet they are routinely expected to carry out complex duties for which they're not being paid.'

Swansea Bay branch secretary, Andrew O'Leary, added: ‘No one wants to be on strike. These undervalued staff would much rather be at work caring for patients, but the health board has given them little other option.'

In response, a Swansea Bay University Health Board spokesman, said: ‘We're disappointed with the ballot for strike action over the banding of our healthcare support workers, an issue that is not unique to Swansea Bay or Wales for that matter.

'We respected their right to ballot and want to emphasise that we value all of our staff and the work they do – not least our healthcare support workers - and are committed to ensuring that everybody is treated fairly.'