The Green Party is calling on the Alward government to establish a royal commission to study plans to switch to a shared-risk pension model for public service retirees.
"The province intends to violate its role as trustee by abandoning retroactively its commitments to pensioners in the public sector," said Norman Laverty, a former superintendent of pensions for the provincial government and the Green Party's advocate for economic and social development.
"It's unacceptable," he said.
Premier David Alward announced plans to overhaul the pension system last May, saying the current plan is not sustainable.
Among the proposed changes, guaranteed cost-of-living increases will be eliminated for pensioners and instead be dependent upon market performance.
In addition, the risk of any market downturns would be shared by both sides instead of being borne by the provincial government alone.
The Green Party wants a Royal Commission on Retirement Income to determine if there truly is a crisis in the funding of retirement income for New Brunswickers in the public and private sectors, and to propose long-term solutions.
"We need to ensure that people in the workforce today have adequate income when they retire," said Green Party Leader David Coon.
"We believe a royal commission of inquiry is the best way to bring clarity to the many complex issues surrounding the future of retirement income."
Last month, Finance Minister Blaine Higgs faced thousands of angry retirees during a series of information sessions held across the province about the proposed changes.
Many pensioners have argued it's unfair for them to lose benefits they've already paid for.
The proposed model also includes increased contribution levels and moving the age of retirement to 65 from 60 over a 40-year period.
The Public Service Superannuation Act (PSSA), which covers employees who work directly for government departments and NB Power, currently has a $1 billion shortfall.
It included 13,441 pensioners as of March 31, 2012. Their average annual pension was $20,603.