Hospitals and health trusts in England have been told by regulators to look again at their financial plans as current ones are unaffordable.
Monitor has written to the 46 foundation trusts with the biggest deficits "challenging" their plans.
It urged money-saving measures such as filling only essential staff vacancies.
The Department of Health supported the move, but Labour argued it suggested there was a financial crisis in the NHS that was "spiralling out of control".
David Bennett, chief executive of Monitor, said the NHS was facing an almost unprecedented financial challenge this year
http://www.bbc.co.uk/news/health-33767791