The C.D. Howe Institute report says the government is underestimating the plans' liabilities by about 40 per cent, or $100 billion, so taxpayers are on the hook for more than advertised.
The report says the changes are an improvement on the current system, but need to go further before an equitable distribution of benefits and risks is achieved.
Under the new law, public servants, members of Parliament and Senators will contribute roughly half of the reported cost service of the plans.
To reach a true 50-50 split between employee and taxpayer obligations, the pension plans would need to be radically altered, the think-tank says, or participant contributions would need to rise further.
The bill received Senate approval on Wednesday and requires only royal assent to become law.