OTTAWA -- One of Canada's biggest banks says sliding oil prices could turn the federal government's promised 2015-16 surplus into a deficit.

A report by TD Bank is projecting Ottawa to run a $2.3-billion shortfall next fiscal year rather than the $1.6-billion surplus predicted by the government in November -- before oil prices fell further.

The bank also says the government's $4.3-billion surplus projection for 2016-17 is on track to become a $600-million deficit unless new revenue-generating or cost-cutting measures are introduced.

TD, however, says the deficit estimates are still smaller than the government's $3-billion reserve set aside for contingencies -- which would help keep Ottawa in surplus territory.

Prime Minister Stephen Harper has promised his government will balance the books in 2015-16 despite tumbling oil prices.

The Bank of Canada is scheduled to address the economic impact of falling oil prices in a speech by deputy governor Timothy Lane.

The TD report also says low oil prices will make it difficult for the Conservative government to deliver on two outstanding 2011 campaign pledges: an adult fitness tax credit and doubling the annual contribution limit on tax-free savings accounts.