The crew stopped work immediately and the company summoned dinosaur experts, CNN reported. The fossil was found near Spirit River in northern Alberta.
Brian Brake, executive director of the nearby Philip J. Currie Dinosaur Museum, told the Edmonton Journal what has come to light so far suggests the fossil is a complete or nearly complete hadrosaur.
"What we have is a totally composed tail," Brake said. "It's beautiful."
A team from the Royal Tyrrell Museum of Palaeontology in Drumheller, Alberta, arrived at the site Wednesday.
The fossil is expected to be taken to the Tyrrell Museum or the University of Alberta once it has been removed, which will be a delicate process.
Matthew Vavrek, a palaeontologist who does a lot of exploring for fossils in northern Canada and who has viewed the fossil, told CNN it's possible the tail may be all that is there: "Sometimes what you see is what you get."
But even that, he said, is a spectacular find.
"The last time I've seen something like that was in a museum. I've never found something like this before," he said.