Facebook CEO Mark Zuckerberg and a host of leading business executives have called on U.S. President Donald Trump to preserve the rights of “dreamers” under an immigration reform program founded by the Obama administration in June 2012.

The Deferred Action for Childhood Arrivals program (DACA), a policy that grants leniency to undocumented immigrants brought to the U.S. as children is currently under review by the Congress. Trump is said to be conflicted on the state of the program, but a group of state attorney generals have said they will challenge the policy in court if Trump does not rescind it by Tuesday, according to Politico.

In an open letter published Thursday, the Facebook founder urged the president to retain the policy, saying that the U.S. economy would lose hundreds of billions of dollars if workers and students currently protected by the scheme were faced with deportation.

It is estimated that some 800,000 citizens could be hit by the proposed reforms.

“Our economy would lose $460.3 billion from the national gross domestic product (GDP) and $24.6 billion in Social Security and Medicare tax contributions,” read the letter, which was posted on FWD.us, an immigration reform group founded by Zuckerberg.

He was joined by the CEOs of Amazon, Google and Microsoft, as well as other business leaders, in signing the letter.

The letter noted that those protected by DACA grew up in the U.S., are registered with the government, and are subject to extensive background checks. More than 95 percent are said to be in school or work, and 5 percent have started their own business.

“I stand with the Dreamers — the young people brought to our country by their parents,” Zuckerberg wrote in a Facebook post late Thursday.

“We need a government that protects Dreamers,” he continued.

“These young people represent the future of our country and our economy.”

Almost three quarters of the top 25 Fortune 500 companies count DACA recipients among their employees.