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John Green, shown here in Dallas, Texas, Jul. 16, 2015, slammed President Trump's decision to rescind DACA. Getty Images

Bestselling author John Green took to Twitter Tuesday to slam President Donald Trump over his decision to rescind the so-called “Dreamers” program. Trump pulled the Deferred Action for Childhood Arrivals, or DACA – a program aimed at protecting immigrants who came to the United States undocumented as children.

“Furious and heartbroken to see the U.S. abandon #DACA, which made our country stronger and more prosperous. To the Dreamers: I’m so sorry,” Green tweeted Tuesday.

Green also retweeted a post urging people to call their representatives to defend the program as well as a video of a school walkout in defense of DACA.

The Obama-era policy shields an estimated 800,000 young people from being deported and allows them to work in the United States legally. Attorney General Jeff Sessions announced Tuesday the administration’s plan to “phase out” the program and pave the way for a new one. The policy would stop accepting new applications for legal status dated after Sept. 5, according to ABC News.

“To have a lawful system of immigration that serves the national interest, we cannot admit everyone who would like to come here,” Sessions said. “It’s just that simple.”

Sessions called the program “an unconstitutional exercise of authority by the executive branch.” Trump implied on Twitter he would put the decision in the hands of Congress.

“Congress, get ready to do your job – DACA!” the president wrote early Tuesday morning, before Sessions made the official announcement.

“Congress now has the opportunity to advance responsible immigration reform that puts American jobs and American security first,” Trump said in a statement.

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John Green, shown here in Dallas, Texas, Jul. 16, 2015, slammed President Trump's decision to rescind DACA. Getty Images