The Trump administration will file paperwork with the United Nations as early as Monday to withdraw the United States from the Paris Agreement, marking the first formal step in a one-year process to exit the global pact to fight climate change.

The move would leave the world's largest historic greenhouse gas emitter as the only country outside the accord, a decision President Donald Trump promised early in his term to unfetter America's domestic oil, gas and coal industries.

"What we won't do is punish the American people while enriching foreign polluters," Trump said at a shale gas industry conference in Pennsylvania on Oct. 23, referring to his planned withdrawal from the agreement.

The United States had signed onto the 2015 pact during the Obama administration, promising a 26-28% cut in U.S. greenhouse gas emissions by 2030 from 2005 levels.

Trump campaigned on a promise to rescind that pledge, saying it would unfairly hurt the U.S. economy while leaving other big polluters like China to increase emissions. But he was bound by U.N. rules to wait until Nov. 4, 2019 to file the exit papers.

The State Department is expected to submit the letter to United Nations Secretary General Antonio Guterres, starting the clock on a process that would be completed just one day after the 2020 U.S. presidential election, on November 4, 2020.

By Monday afternoon, no letter had been submitted. Officials for the White House and the State Department did not comment on when the paperwork would be filed.

All of the top Democratic presidential hopefuls seeking to unseat Trump in next year's election have promised to re-engage the United States in the Paris Agreement if they win.

But Trump's withdrawal from Paris could still leave a lasting mark, said Andrew Light, a senior fellow at the World Resources Institute and former adviser to the U.S. climate envoy under President Barack Obama.

"While it serves the political needs of the Trump administration, we will lose a lot of traction with respect to U.S. influence globally," he said, adding it could take time for the international community "to trust the U.S. as a consistent partner."

Until its formal exit, the United States will continue to participate in negotiations over the technical aspects of the agreement, represented by a small team of career State Department officials.

The United States and China, the world's two largest carbon emitters, have recently been leading negotiations of the Paris "rule book" that outlines transparency and reporting rules for signatories.