Trans Mountain Corp. is preparing to officially start construction on its pipeline expansion after years of delay.

On Tuesday, Trans Mountain president and CEO Ian Anderson, federal Natural Resources Minister Seamus O'Regan, provincial Energy Minister Sonya Savage, as well as representatives from local governments and the Enoch Cree Nation will officially mark the start of construction at an event near Acheson, Alta., west of Edmonton.

The Crown corporation that owns the project has already mobilized its workforce and restarted some work at the pipeline's terminals, since the federal Liberal government approved the $7.4-billion expansion for the second time earlier this year.

The Federal Court of Appeal is currently reviewing an appeal by Indigenous groups of that second approval.

Alberta Premier Jason Kenney has called on Prime Minister Justin Trudeau frequently to push ahead with construction on the project, and blamed the federal Liberals for delays. The two are set to meet in Ottawa next week.

Trans Mountain has said it expects 4,200 workers to be employed along the pipeline corridor by the end of the year.

The pipeline expansion will carry 890,000 barrels of oil per day, tripling its capacity, from Alberta to the B.C. coast once completed.

It's set to be finished by mid-2022.