Opponents of the Keystone XL tar sands pipeline set themselves a new challenge on Monday – to gather 500,000 signatures in a single day – and block Congress from reviving the project.

Barack Obama formally rejected the proposed pipeline last month, elevating a once obscure project to a leading issue in the 2012 elections.

But Republicans in Congress are due on Monday to introduce a new measure that would force work to begin on the pipeline, essentially overturning the White House decision.

Opponents of the pipeline are fighting back, with author and activist Bill McKibben's 350.org group announcing a new drive by some three dozen green and business groups to recruit 500,000 signatories in a single day to an anti-pipeline petition.

McKibben said environmental groups had to defend their victory as President Obama and Democrats came under fire for blocking the pipeline. "It is clear that the fossil fuel industry is in an all-out push to get this done. Big oil never loses and they are determined to ram this thing through," he said in a phone interview. But he argued the election year fight over the pipeline could ultimately help Obama's chances of being re-elected to the White House.

"We are sending a message to the Senate leadership that the president actually did something brave here so back him up," he said. "I think it's clear that as the president has taken bold stands in the last few months its has helped - not hurt - him. Clearly the oil industry is going to run ads about Keystone in the elections. It is time to make a forthright defense again."