TransCanada aims to build an extension to the Keystone oil pipeline in order to ship so-called tar sands oils to refineries along the southern U.S. coast.
The Canadian National Energy Board, in a letter to the company, said it was "concerned" by the company's safety record. The regulator said it would "not hesitate to take appropriate corrective actions" should it uncover violations.
The NEB was responding to a May letter filed by a TransCanada employee, who is no longer with the company, that said the company wasn't following the letter of the law.
Grady Semmens, a spokesman for the pipeline company, told The Calgary Herald that TransCanada had taken internal corrective actions.
"Many of the claims being made by the former employee relate to non-destructive testing inspections of new pipelines before they were approved for service," the letter stated.
Environmental advocacy groups have expressed concern about the safety of shipping tar sands oil through pipelines. They contend that type of crude oil may be corrosive. A 2010 tar sands oil spill in Michigan by TransCanada rival Enbridge was the costliest onshore incident of its kind in the history of the energy industry.