The company, a unit of Houston-based Kinder Morgan Inc, set a May 31 deadline to decide if it will proceed with the expanded line from Edmonton, Alberta to a port in the Vancouver area, which would give landlocked Canadian crude greater access to foreign markets.

The project's fate will create political ripples in Ottawa, where Justin Trudeau's Liberals have promised the pipeline will be built one way or another, and sway investor confidence in Canada's oil sands, which already produce far more oil than can move on pipelines.

Building more pipelines was a cornerstone of Trudeau's energy policy. But the federal government is increasingly convinced that any assurances Ottawa gives Kinder Morgan will be rejected, said two sources with direct knowledge of the matter. They are not authorized to speak publicly.

Investors and project contractors are also increasingly pessimistic.

"I can't walk out of my office or have a beer with someone where a conversation around this doesn't occur," said Rafi Tahmazian, senior portfolio manager at Canoe Financial, which manages shares of several Canadian oil producers.

"I'm worried - very worried - that (Kinder) will walk away."

Kinder Morgan Canada declined to comment.

If Trans Mountain fails, it would be the third major Canadian export pipeline project to stall in two years, putting greater pressure on Canadian heavy crude prices that already trade at a discount to global prices due to limited transport.

Kinder Morgan set the deadline in part due to frustrations with delays caused by British Columbia government, which is concerned about possible oil spills.

Trudeau has publicly vowed to build the pipeline with or without Kinder, and offered to indemnify the company against losses related to B.C.'s delays.

KML's share price has fallen 9.7 percent since early April, when the company halted all non-essential work, underperfoming a 5 percent rise in the benchmark Canada share index.

"We think the stock itself is pricing in a less than 25-percent chance of the project going ahead," said Matthew Murphy, an analyst with investment bank Tudor, Pickering, Holt and Co.

Danny Mott, owner of Mott Electric, the electrical contractor on Trans Mountain, said he does not think the federal government has done enough to enforce its jurisdiction, nor to crack down on protesters who block access to Kinder Morgan work sites on a near-daily basis.

"If we don't have strong laws and the intent to follow through with them, I wouldn't invest in that. I think I would walk away," he said.

(Reporting by Julie Gordon in Vancouver and Rod Nickel in Winnipeg, Manitoba; Additional reporting by David Ljunggren in Ottawa; Editing by Lisa Shumaker)

By Julie Gordon and Rod Nickel