With the future of the long-form census in jeopardy, Ottawa Mayor Larry O'Brien says the city will find a way to collect the information it needs to deliver services.

Ottawa city council passed a motion last week asking the federal government to reconsider its decision to scrap the mandatory long-form census and replace it with a voluntary one.

But O'Brien said the city will do what it can in the event the federal government doesn't change its mind.

"City planning is based on having accurate information on the citizens...so we need that and we'll collect that one way or another," said O'Brien on Thursday.

O'Brien's assurances come a day after city coucillors and staff suggested a back-up plan may not be possible.

"I'm not sure that there is a viable contingency plan," said Councillor Peter Hume.

"For us to step in the gap is going to be incredibly expensive and incredibly difficult," said Hume, who is also president of the Association of Municipalities of Ontario.

Ian Cross, who is in charge of Ottawa city's strategic forecasting, said it would be "impossible" for the city to collect the same data found in the long-form census.

"My group has six [people], they have 6,000 people at StatsCan," said Cross. "We're not specialised to do that [and] we don't have the skills to do that."

Cross said they'll be forced into guesswork, using old data to decide how to spend tax money on services such as transportation and health.

"It will have a very drastic effect on city operations," said Cross.

Since Industry Minister Tony Clement announced in late June the decision to end the mandatory census, statisticians, researchers, academics, religious groups and others have decried the move, arguing it will result in skewed and unreliable data.

On Wednesday Munir Sheikh, the head of Canada's national statistical agency, resigned in protest, saying in a letter a voluntary survey cannot be a substitute for the mandatory form.