Plans at Westminster to raise the retirement age for teachers are being contested by the Scottish Secondary Teachers' Association.
As the SNP called on the Scottish Executive to distance itself from pension proposals south of the border, the SSTA warned serving teachers under the age of 49 to expect difficult financial choices in the coming year.
David Eaglesham, the union's general secretary, said that raising the pension age from 60 to 65 from 2006 for new entrants and from 2013 for serving staff would hit hard.
"It will also have a major impact on future recruitment of new staff which may in turn lead to a shortage of teachers and part-time education," Mr Eaglesham said.
Members are also being warned that they may have to raise their contributions as more teachers live longer in retirement.
"In 1981, the average life expectancy of a male teacher at age 60 was 80 years of age. By 2001, this had risen to 86 years of age. For women teachers, the equivalent figures were 84 and 88.5 years of age.
"The burden of this on the pension scheme is very considerable and is unlikely to reduce over coming years as health standards continue to rise," Mr Eaglesham said.
Fiona Hyslop, SNP shadow education minister, said that the Westminster Green Paper - Simplicity, Security and Choice - was in direct contradiction to the post-McCrone agreement, which had backed a winding-down scheme for teachers in their mid-50s.
Ms Hyslop said: "A recent circular from the Scottish Public Pensions Agency shows that steps have already been taken to raise the age at which teachers get their pensions. Far from implementing the McCrone agreement, here is a Scottish Executive agency working against it."
She appealed for ministers to protect the agreement. "The Executive has the power to act. The pensions agency is an executive agency of the Scottish Executive and the Scottish Executive can direct it, if it so chooses, to implement the McCrone retirement clauses in full.
"We also heard in (the) statement on the local government finance settlement that responsibility for teachers' pensions is transferring from the Treasury. The power is there, all that is needed now is the political will and courage to use it."