Trump said Monday he will sign an executive order that would remove the right to citizenship for babies of noncitizens and undocumented immigrants born on U.S. soil.
"It was always told to me that you needed a constitutional amendment. Guess what? You don't," Trump said in the interview by Axios on HBO, the news site's new documentary series.
"We're the only country in the world where a person comes in and has a baby, and the baby is essentially a citizen of the United States ... with all of those benefits," Trump said. "It's ridiculous. It's ridiculous. And it has to end."
"It's in the process. It'll happen ... with an executive order."
However, Canada and many other countries grant birthright citizenship.
Opponents will argue that it's not within the president's power to change birthright citizenship.
The 14th Amendment to the Constitution says:
"All persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States and of the State wherein they reside."
Trump's comments come as he continues to push a hard anti-immigration line ahead of next week's midterm elections. On Monday, the Defense Department announced plans to deploy 5,200 active duty troops to the U.S.-Mexico border by end of the week as a migrant caravan made its way north from Central America.
Trump said he had run the idea of ending birthright citizenship by his counsel and plans to proceed, despite the likely uproar. However, during the interview, Trump expressed surprise that Axios knew about his secret plan: "I didn't think anybody knew that but me. I thought I was the only one," he said.
Correction: This story was revised to correct the timing of the midterm elections.
— CNBC's Marty Steinberg contributed to this story.