Apple Inc.  (AAPL - Get Report) CEO Tim Cook said immigration is the paramount issue America faces at the moment, calling the future of DACA "the biggest issue of our time."

Cook spoke passionately about the importance of immigration and protecting DREAMers -- undocumented immigrants who came to the United States as children -- at the Bloomberg Global Business Forum in Manhattan on Wednesday.

"We're pushing extremely hard on this," he said. "This is, I think it's the biggest issue of our time currently, among all these big issues, because this goes to the values of being American. This is are we human, are we acting in a track of morality."

President Donald Trump earlier this month decided to end the Obama-era Deferred Action for Childhood Arrivals program, or DACA, that grants work permits to undocumented immigrants who arrived in the United States as children, with a six-month delay. He has said he will "revisit" the issue if Congress fails to address it through legislation.

Trump's wavering on DACA has put the lives of the estimated 800,000 young people registered in the program in disarray and under the threat of deportation.

"They love America deeply," Cook said on Wednesday. "I wish everyone in America loved America this much."

DREAMers "have jobs, they pay taxes, they're pillars of their communities, they're incredible people," he said. "This is unacceptable. This is not who we are as a country, and so I am personally shocked that there's even a discussion of this."

Former New York City Mayor Michael Bloomberg, the host of the forum who appeared alongside Cook, echoed his alarm. "What on earth are we thinking about?" he said. "We desperately need them."

"We can and must every day expand the definition of us, shrink the definition of them," former President Bill Clinton said at the opening of the event.

None of the men named Trump, whose Trump Tower is just a few blocks away from the Plaza Hotel where they were speaking, but their implicit criticism of him was clear.

"Words have consequences," Bloomberg said, alluding to the president's anti-immigrant rhetoric. "We need a constant source of new blood coming into this country, and if they can't come here, they'll go someplace else that's more welcoming."

Business leaders have been a strong voice in urging Trump and Congress to take action on DACA and protect DREAMers. Cook took to Twitter as news of Trump's decision broke to speak out.

250 of my Apple coworkers are #Dreamers. I stand with them. They deserve our respect as equals and a solution rooted in American values.

— Tim Cook (@tim_cook) September 3, 2017

"This is about basic human dignity and respect," he said on Wednesday. "It's just that simple and straightforward."

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