Senate Republicans introduced an amendment Monday to a federal transportation bill that would speed the construction and operation of a controversial oil pipeline between Canada and the United States.

The move sparked a backlash from environmentalists, who generated hundreds of thousands of e-mails against the amendment within hours.

It remains unclear how quickly the Senate will vote on the amendment, which has the backing of 44 Republicans and one Democrat. Senate Democratic leaders oppose it and the chamber is embroiled in a separate fight over President Obama’s contraception coverage policy.

The amendment indicates the debate over TransCanada’s Keystone XL pipeline — which would transport heavy crude from Canada’s oil sands to Gulf Coast refineries — will continue to help define the two parties this election. Proponents say it will create jobs and provide the United States with a reliable energy supply. Opponents argue that the energy-intensive extraction of crude in Canada will accelerate climate change, and they worry that a spill could jeopardize sensitive habitat.

President Obama denied the TransCanada permit application last month, saying a congressionally mandated deadline did not allow his aides enough time to evaluate the project once Nebraska completed a rerouting of the pipeline around the sensitive Sand Hills habitat. The firm has indicated it will reapply for a federal permit.

The measure sponsored by GOP Sens. John Hoeven (N.D.), Richard G. Lugar (Ind.) and David Vitter (La.) would eliminate the need for TransCanada to obtain a federal permit to cross the U.S.-Canada border, while allowing Nebraska unlimited time to develop an alternative route through its territory.

Hoeven said that the measure “not only acknowledges the vital national interest this project represents on many levels, but also works in a bipartisan way to begin construction.”

More than 30 environmental and liberal groups began a noon drive to muster at least half a million messages to Congress within 24 hours in opposition to the project. They reached that goal just before 7 p.m. They planned to deliver those and later messages Tuesday to the offices of Senate Majority Leader Harry M. Reid (D-Nev.) and Minority Leader Mitch McConnell (R-Ky.).

“Anyone who thought environmentalists were graying into irrelevance was wrong,” said climate activist Bill McKibben, who co-founded the group and had helped lead protests against the pipeline.

But Lugar spokesman Neil Brown said that Republicans would continue pressing for approval of the project. “We are committed to succeed where President Obama failed on Keystone XL, so we’ll try every avenue to get a vote and keep coming back on KXL until we get a vote for jobs,” he said.