The union representing thousands of government staff has reacted angrily to news its members will have to pay more for their pensions in future, for fewer benefits.
Last week, government announced the cost of pensions for some 8000 public sector workers would have to be met by a phased 3% increase in contributions.
A package of measure to reduce a 23% shortfall between monies paid into the scheme and the cost of providing pensions will be debated in Tynwald next month.
They include a rise in the minimum retirement age, an increase in employer contributions and for new members, longer working before pension benefits are available.
Government staff cutbacks resulting in fewer people paying in and more drawing their pensions, are among factors blamed for the latest crisis.
Prospect, which has a diverse membership, says major reforms brought in with the Government Unified Scheme two years ago should have solved long-term funding issues.
Union boss Angela Moffatt says a serious and very expensive miscalculation has been made:
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