Health Secretary Andrew Lansley believes pension changes to be "unrealistic", a leaked letter shows.
In a letter to Treasury Chief Secretary Danny Alexander, Mr Lansley criticised the assumption that NHS workers should work for 48 years before receiving their pension, when the current average career is 18 years.
The letter said: "In the NHS currently, the average full-time career for those taking a pension is only 18 years and it seems unrealistic to suggest that pension scheme design should be based on the assumption that a predominantly female workforce would need to work full-time, 48-year careers in future to receive a full pension.
"It is also difficult to see how this meets our commitment to maintain gold-standard pensions."
Mr Lansley's reaction came after a briefing document outlined the reforms to cabinet members.
Mr Lansley also warned that industrial action over the pension reforms was a "real risk".
Trade Unions have already been on strike over pension reforms and further strike action has been suggested.
A spokesperson for Unison, a public service trade union, told BBC: "The move to make public sector workers pay more into their pensions, work longer and get less, is driven by ideology - that is the Treasury wants to use the money saved to pay for the country's deficit."
Under the current reforms, public sector workers will be expected to retire later, contribute a higher percentage of their salary to the scheme receive an average career salary pension rather than a final salary one.
Lansley added that there is a risk workers will "simply opt out".
"In the NHS, if it appears that we intend to significantly reduce the value of future accrual we also face the risk of opt-out from higher-paid groups as well as the lower-paid.
"GPs for instance pay both employer and employee contributions and can choose to invest them elsewhere or take them as pay.
"This would create a significant fiscal pressure in the short to medium term and in respect of lower-paid staff who opt out would increase pressure on the social security budget in the longer term."
The Department of Health responded to the leak, saying that the reform proposals had developed since Mr Lansley wrote his letter. A spokesperson said: "Less than 10 days ago the whole of the cabinet signed up to the need for pension reform and agreed to further talks taking place on a scheme-by-scheme basis.
"The government is committed to public service pensions remaining among the very best available."
Shadow work and pensions secretary Liam Byrne told the Telegraph: "We now know that there is a deep split at the heart of government on these pension negotiations.
"People will want to know why Andrew Lansley has sat on his hands when he secretly believes that other cabinet ministers are seeking a head-on confrontation with public sector workers.
"This is chaotic and reckless government."