Health Secretary Andrew Lansley has privately attacked the Government's public sector pension shake-up, it has been revealed.
In a letter to Treasury Chief Secretary Danny Alexander, he condemned elements of the reforms as "inappropriate" and "unrealistic".
The changes would hit women health workers particularly hard, and do not meet the coalition's "commitment to maintain gold-standard pensions".
The damning critique, obtained by the Daily Telegraph, was penned two months ago after a paper describing the proposals was circulated to the Cabinet.
Mr Lansley's views are likely to be seized on by unions, who have threatened national strikes over the controversial issue in the autumn. Previously Tory ministers were thought to be supportive of the plans.
Under the reforms outlined by Liberal Democrat Mr Alexander last month, public sector workers will retire later, contribute more to pensions, and receive payouts based on average career earnings, rather than final salary.
The letter from the Health Secretary - who oversees Britain's biggest public sector employer - was sent two months ago.
Referring to the document distributed to ministers, he said the paper "assumes that public sector workers, many of whom are women, will work a 48-year career" to get a full pension and that "it is also difficult to see how this meets our commitment to maintain gold-standard pensions".
Mr Lansley criticised other parts of the proposed reforms for being particularly unfair to NHS workers. Many health workers already pay more for their pensions than civil servants or other Government employees.
"We face a real risk, if we push too hard, of industrial action involving staff groups delivering key public services," he wrote. "There is also the risk that lower-paid staff in particular will simply opt out, leaving HMT (HM Treasury) with reduced receipts in the short term while still having to pay for past pension promises."
A Department of Health spokesman said: "Things have moved on since this was written. Last month the Chief Secretary set out the Government's commitment to protect the low paid and ensure low and middle income earners get a pension at retirement broadly as good as they get now."