Two London hospitals are cutting hundreds of jobs to save money, it has been announced.
Kingston Hospital said there were 486 posts that could go, while St George's Hospital in Tooting has identified 200 posts that will close.
Unison general secretary Dave Prentis said: "This announcement is more proof that the NHS is not safe."
Kingston Hospital, which is applying to become an NHS Foundation Trust, said the cuts were part of a long-term plan.
A spokesperson said: "We expect the reduction of these 486 posts, over five years, to be managed as part of natural staff turnover, as on average, we see between 300 and 400 staff leave the trust each year."
Meanwhile, a spokesman for St George's Healthcare said: "So far we have identified 200 posts that will go but are planning to avoid compulsory redundancies with those staff affected being redeployed into existing vacancies.
"We have rigorous quality control at a ward and clinic level to ensure that changes are made safely."
Unison general secretary Dave Prentis said: "Cutting jobs and closing at least three wards is a devastating blow for staff and patients at St George's.
"This announcement is more proof that the NHS is not safe in David Cameron and Andrew Lansley's hands and is reminiscent of Margaret Thatcher's devastating reforms during the '80s and '90s.
"Only two weeks ago, Barts and The London announced 630 job losses, including 250 nurses and 100 beds cut."
St George's hospital has a 20% staff turnover every year and its total budget last year was £418m.
A spokesman for the St George's hospital NHS trust, which employs 7,000 people a year, said: "We have been open with staff and unions about the need to achieve £55m savings during 2011/12."
Meanwhile, a Kingston Hospital spokesman said: "We are in the process of applying to become an NHS Foundation Trust.
"As part of our application, we have to put together a long-term plan, which shows how we are going to manage with 25% less money, over the next five years.
"These plans have been put together at divisional level, by clinical teams."
But Unison warned that frontline staff would be affected.