Northeastern lawmakers are planning to ask the Obama administration to require an extensive environmental review process for any efforts to utilize an existing pipeline to ship crude oil produced at Canada’s tar sands to Maine.

Led by Rep. Chellie Pingree, D-Maine, the lawmakers are drafting a letter to freshly minted Secretary of State John Kerry calling for a new presidential permit and full environmental impact statement should the operators of the Portland-Montreal Pipeline attempt to ship tar sands crude to Maine through the decades-old conduit.

The pipeline currently carries crude oil from Maine to Montreal, but in 2008 the Portland Pipe Line Corporation, or PPLC — one of the entities that manages the 230-mile pipeline —sought permission from the State Department to reverse its flow to carry Canadian crude oil to Maine for export.

The dispute opens a new front in the controversy surrounding the Keystone XL pipeline, designed to carry crude from the Alberta tar sands to Gulf Coast refineries. President Barack Obama is under pressure from the oil industry and construction workers to approve the project. Environmentalists are pushing the White House to reject the pipeline, arguing that the energy-intensive process of producing oil from the tar sands would drastically boost greenhouse gas emissions.

Critics say the aging Maine-to-Quebec pipeline, which crosses Vermont and New Hampshire, was not designed to carry the heavier, more viscous bitumen produced from the western Canadian “tar sands.” According to the lawmakers’ letter, the State Department at the time indicated that reversing the pipeline’s direction would not require new presidential permission or an additional environmental impact statement.

“We believe that a changeover to carrying tar sands is a significant alteration in function and environmental risk for existing pipelines, and that the State Department should require a new permit and environmental review for these changes to occur,” states the draft letter, which is currently signed by Rep. Michael H. Michaud, D-Maine, Rep. Carol Shea-Porter, D-N.H., and Sen. Bernard Sanders, I-Vt.

While the lawmakers acknowledge that PPLC is not currently seeking State Department approval to reverse the pipeline’s course, the letter notes that efforts are underway in Canada to reverse the direction of related pipelines.

Those efforts could intensify if Obama should reject the proposed Keystone XL pipeline.

The State Department is currently completing a supplemental environmental review for an alternate route for the pipeline in Nebraska. Obama cited the study last year to delay a final decision on the presidential permit needed to cross the U.S.-Canadian border. That ruling may come in the next few months, but environmentalists plan to remind Obama of their intense opposition to the pipeline with a large-scale rally Sunday on the National Mall.