The union's new report, Less Fit for the Future, shows NHS providers ran up a combined deficit of more than £1.1bn last year.
Unison head of health Helga Pile said: ‘Cutting thousands of NHS jobs is the wrong answer when staff are already stretched to breaking point.
‘The NHS is being asked to transform how care is delivered, with more community services and technology. But none of this is possible without the staff to make it happen.'
The union's research revealed trusts are planning cuts to at least 3,600 clinical roles including many nurses and other clinical staff, as well as support post reductions through vacancy freezes, restructuring and reduced use of agency workers.
Nearly two-thirds (65%) of NHS staff said job cuts have led to an increase in their workload, while the same number (65%) reported rising stress levels.
Almost half of staff (47%) reported that systems and processes were slower following job cuts or vacancy freezes, while a worrying 42% said patients were receiving a worse service.
A Department of Health and Social care spokesperson said: ‘Thanks to the extra £26bn we have invested, the NHS has an extra 12,000 doctors, 16,000 nurses and 8,000 mental health workers compared to July 2024.
‘We make no apology for reducing spend on agency staff, for which the NHS was previously paying huge sums to rip-off recruitment agencies. It is only because of that focus on getting better value for money that we have been able to invest in more frontline staff, give staff above forecast inflation pay rises for two years in a row, and improve services for patients.'
