The NHS is facing an almost unprecedented financial challenge this year, and current plans are quite simply unaffordable, a health chief has warned.
Foundation trusts have been asked to revisit their plans by the chief executive of the regulator, Monitor.
David Bennett wrote to trusts telling them: "We are already reviewing and challenging the plans of the 46 foundation trusts with the biggest deficits.
"However, it is clear that this process will not close the funding gap and so we need all providers - even those planning for a surplus this year - to look again at their plans to see what more can be done."
He asked all trusts to take a further look at their plans, including such areas as ensuring vacancies are filled only where essential, and ensuring that the existing acute inpatient safe staffing guidance "has been adopted in a proportionate and appropriate way" and that rosters are rigorously managed to deploy staff efficiently across all required shifts including evenings and weekends.
Shadow health secretary Andy Burnham said: "This is a sign of a serious deterioration in NHS finances. It suggests that the financial crisis in the NHS is threatening to spiral out of control and hit standards of patient care.
"The suggestion that hospitals can ignore safe staffing guidance will alarm patients and the Government must decide if it will overrule this advice.
"Morale in the NHS is already at an all time low and doctors have lost confidence in the Health Secretary.
"It will raise further questions about how the Government can possibly fulfil commitments on a seven-day NHS without the money to back it up."
The provider sector has forecast a total deficit of more than £2 billion for 2015-16, according to specialist resource Health Service Journal.