Moody's said Thursday that Saskatchewan also has a large pension deficit, but noted it has closed its defined-benefit plans and takes a pay-as-you-go approach to funding them.
"In both Quebec and in Newfoundland and Labrador, relatively large unfunded pension liabilities pose a challenge as they are likely to continue to rise for multiple reasons," Moody's analyst Michael Yake wrote in a report.
The report said average asset returns have been lower since 2008-09, while the discount rates which are used to calculate liabilities have fallen and the average life expectancy of pensioners is rising.
Saskatchewan and Newfoundland and Labrador had the highest ratio of unfunded liabilities to revenues at 55 per cent, while Quebec stood at 49 per cent, it said.
Ontario was the best positioned as the only province with a small surplus.
"We believe that credit risk tied to pensions is manageable because of the relatively small size of unfunded liabilities as a share of revenue and because we expect the provinces that are facing the highest liabilities to enact reforms," Yake wrote.
"If they do not, then credit risk could rise."
The provinces are not alone in facing the problem of underfunded pensions in the wake of the financial crisis.
Several of the biggest names in corporate Canada also face deficits in their employee pension plans, forcing them to put millions into the plans.
Canadian Pacific Railway (TSX:CP), Canadian National Railway (TSX:CNR), Bell Canada (TSX:BCE), MTS Allstream (TSX:MBT), Canada Post and NAV Canada have all lobbied Ottawa in hopes of gaining some measure of funding relief for their pension plans.
Air Canada struck a deal earlier this year to give it some help, but the reliefe came with rules that set limits on executive pay and prevent it from paying dividends to shareholders and buying back stock.