TORONTO -- A who's who of North America's business leaders are turning the screws on the Obama administration to approve the Keystone XL pipeline.

They've sent a letter to U.S. President Barack Obama urging him to approve the controversial pipeline problem.

The letter is signed by more than 165 CEO's and presidents of companies ranging from Boeing to AT&T to Caterpillar Inc. and ExxonMobil.

The letter says the decision on Keystone will affect both investor confidence and the ability of the U.S. economy to speedily grow.

There has been intense opposition to Keystone, which would ship crude oil from Alberta to the U.S. Gulf Coast.

But the letter, dated Oct. 9, says it's possible to manage the environmental risks that many people are concerned about.

"Those risks, like those incumbent in many other significant projects, must -- and can -- be managed, through appropriate regulation and careful stewardship," the letter states. "Keystone XL will meet nearly 60 special conditions set by regulators to minimize risks, and ultimately the net environmental impact of the pipeline would be minimal."

"We urge you to approve the construction of the Keystone XL pipeline to signal to the world that the necessary ingredients for a strengthened U.S. recovery are in place and bolster the foundations of U.S. competitiveness and energy security," the letter concludes.

Trans-Canada Corporation (TSX:TRP) issued a news release Thursday night, expressing its satisfaction with the fact the letter was sent to Obama.

The temperature on Keystone has risen in recent weeks with Prime Minister Stephen Harper vowing that Canada would not take "'no' for an answer until the project is approved.

The majority of Republicans in the House of Representatives, and some Democrats, have long been staunch supporters of Keystone XL. Last year Republicans pushed a mandate through Congress demanding Obama approve the $5.3-billion pipeline within a strict deadline.

But the State Department was still assessing the project amid concerns from the state of Nebraska that Keystone XL posed risks to a crucial drinking water aquifer.

The president invited TransCanada to submit another application, one that would reroute the pipeline around the aquifer.

Environmentalists argue that approving Keystone XL will encourage oilsands crude production, which emits more carbon into the atmosphere than conventional oil production.