Teachers will be "ready to respond" with industrial action if the next Government "declares war" on unions over their final-salary pension scheme, the NUT's annual conference will hear.
Delegates are expected to round on politicians and newspapers that have suggested there should be a review of public sector pensions.
Teachers are concerned, particularly if the Tories gain office, that their so-called "gold plated" pensions will come under attack in a bid to cut a growing #163;25 billion annual bill for public sector pensions.
The Teachers' Pension Scheme is currently in deficit, prompting concerns that it may no longer be sustainable.
Robert Wilkinson, 62, a recently retired teacher, will say the current financial climate could prompt the Government to cut the final-salary element of teachers' pensions, raise teacher contributions and make it impossible to retire on ill-health grounds.
Tory leader David Cameron has already voiced concern about "pensions apartheid", as most workers in the private sector have already lost their final-salary schemes.
Vince Cable, deputy leader of the Liberal Democrats, said last year that public sector pensions were "in danger of running out of control".
Mr Wilkinson said: "We want peace, but if the Government after the election declares war on us, we will respond.
"What people don't seem to understand is that this is our money that we have put away for the future. It is an unfunded pension, not invested in the stock market. We forgo high wages in return for our pensions - it is deferred gratification.
"If they erode our pensions, they are robbing us to pay the bankers."
Unions argue that inequalities between private and public sector pensions need to be dealt with by improving the private sector schemes, not cutting back on state employees' perks.
Mr Wilkinson will complain that it is already almost impossible to retire on grounds of ill-health without being penalised with a reduced pension.
In 1996-97, 5,400 teachers made successful applications, but the figure dropped to 700 in 2007-08.
Teachers are currently allowed to receive a final-salary pension based on the three highest-paid consecutive years they have worked in the decade leading up to retirement, allowing some to "wind down" their careers without a penalty.
Before his speech, Mr Wilkinson told The TES: "There are increasing numbers of teachers and headteachers suffering from mental illness and stress-related illness and I don't want to see them not having that benefit."
The retirement age for teachers joining the pension scheme since 1997 has been raised from 60 to 65, but campaigners say this does not take into account the pressures of the job.
He said pensions were an issue that brought all the teacher unions together "like no other" and that they were likely to join forces to resist any change for the worse.
Michael Gove, shadow schools secretary, told the ATL conference this week that there would be changes to the pension scheme irrespective of which party formed the next government because of the economic constraints.
But he hinted that, under the Tories, changes would only apply to new entrants to the profession.
Pensions will be just one of the heavyweight issues on the agenda at this year's annual NUT conference in Liverpool, which runs from today until Tuesday.
Heated debates are expected over activists' calls for the abolition of Ofsted and the controversial "licence to teach", as well as the use of enhanced disclosures by the Independent Safeguarding Authority.