WASHINGTON, D.C. — Young people currently shielded from deportation and allowed to work legally under the federal program for those brought into the country illegally as children will begin losing their protection in March unless Congress acts before then, the Trump administration announced Tuesday.

In the meantime, the administration will continue to renew two-year work permits as they expire but will stop accepting new applications for the program.

The decision allows President Donald Trump to say that he is fulfilling a campaign pledge to end the Deferred Action for Childhood Arrivals program, which President Barack Obama established in 2012, while also attempting to shift responsibility to Congress for the effect on the nearly 800,000 people covered by the program.

Trump emphasized that effort in an early-morning tweet: “Congress, get ready to do your job — DACA!”

Under the administration’s plan, several thousand people a week would begin losing their legal right to work in the U.S. as of March 6. But because current permits will be renewed until then, the program would not be fully phased out until March 2020.

DACA shields the so-called Dreamers — a politically attractive group for whom Trump in recent months often has expressed sympathy, despite his campaign vow.

“I do not favor punishing children, most of whom are now adults, for the actions of their parents,” Trump said in a statement released by the White House on Monday, after he had Attorney General Jeff Sessions announce the halting of the program on live television from the Justice Department.

“We must also recognize that we are a nation of opportunity because we are a nation of laws,” Trump said, adding that he wanted “a gradual process” to “provide a window of opportunity for Congress to finally act.”

Trump notably left it to Sessions to make the announcement, and had not scheduled any major public appearances Tuesday.

Tossing the issue to Congress could create a serious split among Republican lawmakers. Many Republican leaders, including Speaker Paul D. Ryan of Wisconsin, have said they favor a measure to give permanent legal status to the Dreamers. But many rank-and-file Republicans oppose the idea, which is why past measures failed in Congress, prompting Obama to issue his executive order in 2012.

In a statement, Ryan called Obama’s order perhaps “well-intentioned” but “a clear abuse of executive authority,” and said, “It is my hope that the House and Senate, with the president’s leadership, will be able to find consensus on a permanent legislative solution that includes ensuring that those who have done nothing wrong can still contribute as a valued part of this great country.”

Sessions said that Obama’s action in creating the program went beyond his legal authority, and the Department of Homeland Security “should begin an orderly and lawful wind down.”

Obama’s DACA order was an “unconstitutional exercise of authority by the executive branch,” said Sessions, who has been one of the administration’s leading opponents of the program and a vocal critic of immigration generally going back through his prior years in the Senate.

“The Department of Justice cannot defend this overreach” in court, he added. Several Republican state attorneys general have threatened to challenge the program in court if the Trump administration did not take action to dismantle DACA by Tuesday.

“We cannot admit everyone who would like to come here,” Sessions added. “The nation must set and enforce a limit on how many immigrants we accept each year, and that means all cannot be accepted.”

Obama, in a rare critique of his successor, strongly disputed Sessions’ reasoning in a statement on his Facebook page. He wrote that his administration relied “on the well-established legal principle of prosecutorial discretion, deployed by Democratic and Republican presidents alike.”

He did so, Obama wrote, after Congress ignored his pleas for a legislative solution to shield the so-called Dreamers from deportation — “because it made no sense to expel talented, driven, patriotic young people from the only country they know solely because of the actions of their parents.”

Trump’s action “isn’t required legally. It’s a political decision, and a moral question,” Obama said, adding: “Ultimately, this is about basic decency. This is about whether we are a people who kick hopeful young strivers out of America, or whether we treat them the way we’d want our own kids to be treated.”

Monday, the day before the deadline set by the conservative attorneys general in nine states, Sessions formally wrote to Elaine Duke, acting secretary for the Department of Homeland Security, saying that the underlying legal justification for DACA was flawed and he had determined it would not stand up to judicial scrutiny.

After receiving Sessions’ legal analysis, Duke rescinded the June 2012 memo by Janet Napolitano, Obama’s Homeland Security secretary, that created the program. On Tuesday, Duke instructed the agency that runs DACA, U.S. Citizenship and Immigration Services, to phase it out.

As a result, beginning March 6, the approximately 800,000 people now enrolled in the program will lose their protection from deportation on a rolling basis, as their two-year permits expire.

The Citizenship and Immigration Services agency will continue to process all renewal applications and first-time applications received before Trump’s rescission. As of Aug. 20, 106,341 cases were in the pipeline, including more than 34,000 people applying for a first-time grant.

For the more than 200,000 people whose grants expire between now and March 5, the agency is providing a one-month window, until Oct. 5, to apply for a renewal. More than 55,000 of those people have submitted requests for renewal.

An additional 275,344 people have deferrals that will end during 2018, and 321,920 others have protection that will lapse during the first eight months of 2019.

Duke, the acting Homeland Security secretary, said the courts might have halted the program suddenly, and to avoid that, the Trump administration chose to end it gradually.

“As a result of recent litigation, we were faced with two options: wind the program down in an orderly fashion that protects beneficiaries in the near-term while working with Congress to pass legislation; or allow the judiciary to potentially shut the program down completely and immediately. We chose the least disruptive option,” Duke said in a statement.

Trump repeatedly promised to end his predecessor’s program during an election campaign in which he vowed more broadly to crack down on those in the country illegally, including longtime residents.

But since taking office, Trump has balked at fulfilling that pledge against Dreamers, professing sympathy for their situation that was encouraged by his daughter Ivanka Trump.

In April, he said in an interview with The Associated Press that people protected from deportation under DACA could “rest easy.”

Then in July, aboard Air Force One en route to Paris for Bastille Day celebrations, Trump told reporters he was struggling with what to do about the program.

“It’s a decision that’s very, very hard to make,” he said. “I really understand the situation now. I understand the situation very well. What I’d like to do is a comprehensive immigration plan. But our country and political forces are not ready yet.

“There are two sides of a story,” he added. “It’s always tough.”

Yet, in recent days, as Trump seemed poised to move against the program, its backers in business and politics mobilized to defend DACA in a campaign that included some of the nation’s best-known corporations.

“Dreamers are vital to the future of our companies and our economy. With them, we grow and create jobs,” wrote hundreds of business and tech industry leaders, including executives of Apple, EBay, Crate and Barrel, Microsoft and Starbucks, in an open letter to Trump and congressional leaders.

“As entrepreneurs and business leaders, we are concerned about new developments in immigration policy that threaten the future of young undocumented immigrants brought to America as children,” they said.

The business leaders, organized by the immigration advocacy group Fwd.us, also called on Congress to intervene to ensure that beneficiaries not face deportation.

According to a report from the Center for American Progress, a liberal-leaning advocacy group, 87 percent of beneficiaries are using their work permits and 83 percent of those in school also are working. About 6 percent of DACA beneficiaries have started businesses, the report said, and 12 percent have purchased homes.

Hard-line nationalists in Trump’s inner circle, such as recently removed White House strategist Stephen K. Bannon and senior policy adviser Stephen Miller, had advocated since January that the Trump administration should stop renewing the permits and allow the program to die.

Since Bannon left the White House in August and returned to run conservative media site Breitbart, he’s been pushing from the outside for Trump to halt the program.