The union has warned ministers that there will be no place to hide if they don't clamp down on NHS trusts farming out support services to subsidiary companies - known as SubCos.

Unison tabled a motion, presented by its general secretary Christina McAnea, at the annual union event.

The motion says proposals by health trusts for more outsourcing are a direct contradiction of Labour's pre-election pledge to bring privatised public services back in-house. The union is warning that unless ministers act, there could be strike action in the autumn.

Unison says outsourced staff often have lower pay and worse conditions than workers employed directly by the NHS, and are less likely to have the same access to career opportunities and pensions. It warns that forcing more staff into SubCos will add to the staffing crisis in the NHS and worsen patient care.

Staff employed by Dorset HealthCare NHS Trust, Dorset County Hospital NHS Trust and University Hospitals Dorset NHS are currently being balloted for industrial action over plans to shift hundreds of the lowest-paid health workers to a SubCo. The vote closes on 24 September, just days before Labour Party Conference in Liverpool.

Unison general secretary, Christina McAnea, said: ‘Unfortunately, it appears that SubCos – like zombies – aren't that easy to kill off. NHS England is apparently keen to reanimate a seemingly dead policy. Staff farmed out to subsidiary companies are almost exclusively low-paid. The vast majority are women. And large numbers of them are Black workers.

‘Just like the last time SubCos were on the agenda, we won't take this lying down. The response from Unison and other unions has been uncompromising. The NHS needs to be rebuilt, not dismantled and parcelled off.

‘Ministers cannot hide behind this being an NHS England policy. These developments are happening on their watch. They're in charge, not NHS England, and they have the power to put an end to this right now. If they don't, then they should be prepared to be met with a wave of opposition and industrial action.'

The union has written to all NHS trusts, highlighting the dangers of setting up SubCos,  and reminding senior managers of campaigns fought and won by unions the last time these companies were being used by ‘desperate' health bodies.

NHS England and DHSC were unavailable to comment at the time of writing.