The American political brawl over the approval of TransCanada's proposed Keystone XL pipeline shifted into overdrive on Wednesday as Republicans in the House of Representatives made yet another attempt to take the decision out of U.S. President Barack Obama's hands.

Legislators voted 241-175 in favour of the Northern Route Approval Act, which would give Congress the power to greenlight the pipeline and nix the need for a presidential permit. The bill, however, faces a far less certain future in the Democrat-controlled U.S. Senate.

As legislators debated the bill, their arguments fell along largely partisan lines — Republicans touted the jobs and energy independence that Keystone XL would purportedly spur, while Democrats warned the pipeline poses grave risks to the environment and argued that job creation claims are exaggerated.

One pro-pipeline Democrat — Nick Rahall of West Virginia — said that while he supports Keystone XL and has backed previous pro-pipeline House bills, he could not sign off on legislation that attempts to do away with the permit process altogether.

"Waiving permits for a foreign company? We don't even do that for our domestic companies," he said on the House floor. "This bill's a mockery."

Nineteen Democrats, however, voted in favour of the legislation.

The White House has threatened to veto the bill, saying it "seeks to circumvent long-standing and proven processes for determining whether cross-border pipelines are in the national interest."

Democrats in the House attempted to trip up the bill by way of a handful of amendments, including one that would require any oil and refined product that is transported via Keystone XL to stay in the United States.

Democrats have argued for years that rather than make the U.S. less dependent on oil from hostile OPEC regimes, Keystone XL will allow carbon-intensive Alberta oilsands bitumen to be exported abroad from the Gulf Coast.

Another Democratic amendment would have required Calgary-based TransCanada to disclose its campaign contributions for the past five years before construction of the $7 billion Keystone XL proceeds.

But only one amendment got the green light — one that would require TransCanada to submit its oil spill response plans to the six governors of the states along the pipeline's route.

Constitutional authority

Republicans have long insisted that Congress has the authority under the U.S. Constitution to regulate international commerce — and that includes the pipeline, they say, since it aims to carry bitumen from Canada into the U.S.

On Wednesday, they maligned the Obama administration for taking so long to make a decision on Keystone XL. Nebraska's Lee Terry, the bill's sponsor, called the project "the most studied pipeline in the history of mankind."

Jeff Denham, his Republican colleague from California, added: "When is enough enough? Five years? Six years? Ten years?"

Environmentalists consider the pipeline a symbol of dirty oil, one that will contribute to global greenhouse gas emissions. They've been urging Obama to reject it for years.

They were universal in heaping scorn on the latest Republican attempt to force approval of the pipeline.

"This bill is nothing more than an effort to run roughshod over protections for landowners, wildlife and drinking water supplies so that TransCanada can get oil to Gulf coast refineries for export to China and other countries," said Larry Schweiger, president and CEO of the National Wildlife Federation.

Canadian efforts

North of the border, Prime Minister Stephen Harper's government has nearly doubled its spending on the promotion of Keystone XL, from $16.5 million from $9 million a year ago.

Its beefed-up efforts included Harper's visit to New York last week to pitch the pipeline to the Council on Foreign Relations and in roundtables with U.S. business leaders.

Obama rejected the pipeline early last year, but invited TransCanada to file a new application with an altered route that would skirt Nebraska's ecologically sensitive Sand Hills region.

TransCanada did so, earning the thumb's up from the state of Nebraska and a draft environmental assessment from the State Department that suggested it posed minimal environmental risks. The State Department is assessing the pipeline because it crosses an international border.

The powerful Environmental Protection Agency, meantime, has rebuked State's environmental analysis, saying it's mistakenly concluded that oilsands bitumen would find buyers with or without the pipeline, most likely via rail lines.

The State Department is now reviewing all public comments, including the input from the EPA, before finalizing its draft report. Ninety days after that report, State officials will then determine whether Keystone XL is in the national interest of the United States.

After that, it will be up to Obama to either block or bless the pipeline