TransCanada aims to build Keystone XL to facilitate the delivery of heavy Canadian crude oil to U.S. refineries. A portion of the pipeline from Oklahoma is under construction, though a presidential permit is needed for the cross-border section.
Obama said in an interview published Saturday by The New York Times there was "no evidence" the project would create as many jobs as its supporters claim.
"The most realistic estimates are this might create maybe 2,000 jobs during the construction of the pipeline, which might take a year or two, and then after that we're talking about somewhere between 50 and 100 jobs in an economy of 150 million working people," he said.
James Millar, a spokesman for TransCanada, challenged Obama's position in an email statement, saying the domestic section has already put 4,000 people to work.
"It is not logical to think a $7.6 billion infrastructure project stretching across the entire breadth of the continental U.S. wouldn't employ thousands of workers both in the manufacturing sector and in constructing the pipeline," he said.
Obama said earlier this year he'd weigh the pipeline against its environmental footprint. Canadian oil is viewed as more carbon-intensive to produce than conventional crude, though TransCanada says the environmental consequences are minimal.