The order is the latest hold-up for the Canadian government-owned project, which has been plagued by years of regulatory delay, environmental opposition and massive cost overruns.

Some of the non-compliances include insufficient fencing to protect amphibians and unapproved vegetation clearing, the regulator said in a notice on its website.

The CER issued an Inspection Officer Order to Trans Mountain ordering it to stop work in the wetland until the non-compliances are corrected, investigate their root cause and conduct a safety inspection to confirm the site is safe for work.

Trans Mountain Corp, the Canadian government-owned corporation building the expansion project, said the order applies to a specific work area of about 800 metres.

"Trans Mountain is working hard to correct all non-compliances and to prevent reoccurrence," the company said in a statement, adding it "will seek to have the restrictions under the order lifted as soon as appropriate and according to the law."

Work on the oil pipeline expansion project is more than 95% complete, Trans Mountain said.

The 590,000 barrel-per-day expansion will nearly triple capacity on the existing pipeline running from Alberta to Canada's Pacific Coast. It is due to start operating early next year and will open up markets in Asia and on the U.S. West Coast for Canadian crude.

Prime Minister Justin Trudeau's Liberal government bought the pipeline in 2018 to ensure the expansion project went ahead. However, the cost has more than quadrupled since then to C$30.9 billion ($22.49 billion), partly due to delays in construction.

In 2021, Trans Mountain was ordered to stop work for four months to protect hummingbird nests along a one-kilometer section of its route.

($1 = 1.3747 Canadian dollars)

(This story has been refiled to change the picture.)