"You could have, depending on the activity, up to 6,000 people working on any given day," Howard said. "So you will have 13,000 people working, they just all won't be at the jobs site at the same time."
In November, an analysis by Bloomberg Government compared the number of jobs TransCanada said the Keystone XL would create and the number of jobs the company created when it built another pipeline, simply called the Keystone. That pipeline began operating in 2010 and runs from Alberta to Oklahoma and Illinois.
The Bloomberg analysis found that TransCanada hired an average of 4 to 5 workers per mile to build the first Keystone pipeline. But if the company were to hire 13,000 construction workers for the Keystone XL, the number of workers per mile would rise sharply, to 6 or 7 per mile.
The study concluded that TransCanada either "intends to hire more workers [per mile] for shorter periods of time, or that the company's construction crew and jobs figures are overstated, compared with earlier stages of the Keystone project."
TransCanada did not respond to requests for comment.
Some pipeline supporters have chosen not to get involved in the controversy over the jobs figures. Spokeswoman Jaclyn Houser of Laborers' International said her union "has been focusing on the individual people who would benefit" rather than the overall numbers. "Whether it's 2,000 or 20,000 or 200,000—we're just focused on the fact that 1.3 million construction workers are out of jobs."
In Dec. 2011 the construction industry had a 16 percent unemployment rate, versus 8.5 percent for the nation as a whole.
"If the [pipeline] moves forward it will create thousands of jobs in some capacity," Houser said. "And for a construction worker who's been out of work for months or years, that's a very valuable thing."
Skinner of Cornell agreed that the jobs created by Keystone XL are "by no means insignificant, especially to the working people that receive these jobs."
But Skinner said TransCanada needs to be upfront about the number of jobs and positions that the pipeline could create. The U.S. is facing high unemployment rates, she said, and the problem "should not be trivialized by TransCanada vastly overstating the number of jobs [from] Keystone XL…that's just not fair given that they're creating expectations that can't be met."