Several smaller unions refused to accept the offer
The UK's biggest health service union is to try to renegotiate a pay deal for more than a million workers because of the increase in the cost of living.
Unison says nurses and other NHS workers are struggling to cope with rises in food and energy prices.
The package for staff in England and Wales worth 8% over three years was accepted by its members in June.
The government says this year's deal has been accepted and any renegotiation would have to cover future awards.
A spokeswoman for the Department of Health in England said: "The 2008/09 award has already been accepted and staff have received their increase in pay."
She said any renegotiation would cover 2009/10 and 2010/11.
The pay deal gave staff an increase of 2.75% from April, followed by rises of 2.4% in 2009/10 and 2.25% in 2010/11.
But it was rejected by several smaller unions, including the Royal College of Midwives and Unite, representing ambulance workers, who said it amounted to a pay cut because of rising inflation.
Unison now says it would be submitting evidence to the NHS pay review body under a "re-opener" clause drafted in the event that inflation increased.
It says the deal was on the basis inflation would be around 2%, but the consumer prices index has risen to 3.8%, and Retail Price Index inflation is up to 4.6%.
"Nurses and other health workers are already struggling to cope with almost daily increases in the cost of basic necessities such a food and energy," said Unison's head of health Karen Jennings.
"The re-opener clause was central to this year's multi-year pay talks because it provided a much-needed safety net."