Pro-immigration activists gather in front of the U.S. Supreme Court, April 18, 2016, in Washington. The Supreme Court is scheduled to hear oral arguments in the case of United States v. Texas, which is challenging President Obama’s 2014 executive actions on immigration – the Deferred Action for Childhood Arrivals (DACA) and Deferred Action for Parents of Americans and Lawful Permanent Residents (DAPA) programs.more +

President Barack Obama’s signature immigration action could be immediately overturned when President-elect Donald Trump takes office, leaving its recipients facing uncertainty about their futures.

Obama pushed the deferred action for childhood arrivals (DACA) via executive action to allow undocumented immigrants who came to the U.S. as children to come out of the shadows and pay a fee to receive a temporary work authorization and relief from deportation.

Because this was done via executive action, and is laid out by the Department of Homeland Security, it can be immediately overturned by the next secretary of Homeland Security.

On Monday, Obama urged Trump and the incoming administration “to think long and hard before they are endangering that status of what for all practical purposes are American kids.”

“These are kids who were brought here by their parents. They did nothing wrong. They’ve gone to school. They have pledged allegiance to the flag. Some of them have joined the military. They’ve enrolled in school. By definition, if they’re part of this program, they are solid, wonderful young people of good character,” Obama said during a press conference Monday, his first since the election. “And it is my strong belief that the majority of the American people would not want to see suddenly those kids have to start hiding again. And that’s something that I will encourage the president-elect to look at.”

What Could Happen to Those Who Have DACA?

Those that qualified for DACA had to prove they were under the age of 31 as of June 15, 2012, came to the United States before age 16, lived here for at least five years continuously, attend or have graduated from high school or college, and have no criminal convictions.

Those who qualified and applied, roughly 750,000, were issued temporary status and, separately, a work authorization.

“Everybody is in a state of shock. We don’t know what is going to happen; we don’t know if his extremist nasty rhetoric will go into policy,” David Leopold, an immigration lawyer, told ABC News. “I have corporate clients asking questions they never asked before. Every client is asking how Trump’s election changes things … someone in lawful status, green card holders, people going through legal system or people who are undocumented and have DACA … ‘What do I do now?’ … ‘Am I going to get deported?’”

Trump said on the campaign trail that he plans to end Obama’s executive orders, which would include DACA.

If the Trump administration decides to fully overturn the deferred action policies put in place on Day 1, it would be at the discretion of DHS secretary to determine priorities and whether DACA status is removed together with work permits.

Could DACA Recipients Be Deported Under Trump?

All of the information DACA recipients provided to receive deferred action is held by U.S. Citizenship and Immigration Services (USCIS), which is within the DHS and processes immigration applications, green cards and citizenship.

Immigration and Customs Enforcement (ICE) is also within DHS, and is responsible for enforcing the country’s immigration laws. There are no laws or protections that would block USCIS from handing over all of its information to ICE, which ICE could in turn use to deport people.

"There is currently a memorandum that says that information will only be used in limited circumstances, such as going after criminals, and that memorandum could very well be revised by a new administration. So people are very insecure," Toni Maschler, a D.C.-based immigration attorney, told ABC News. "So long as that policy memorandum continues to exist, there is something that says it shouldn’t be used that way."

In 2011, the administration changed its "notice to appear" policy so people who applied for immigration benefits and were denied were not automatically placed in removal proceedings. Previously, if any individual applied for immigration benefits through USCIS and was denied those benefits, they were automatically transferred to ICE and issued a "notice to appear" in immigration court to begin formal removal proceedings. In order to keep DHS/ICE removals in line with priority cases such as criminals and recent arrivals, the process was changed, with deportation procedures only issued for individuals who met those priorities. USCIS is able to turn information over to ICE at its discretion.

"Unfortunately, I don’t think there is any kind of a stopple that can be used to say, ‘OK because this information was given in good faith, it should not now be used in a retaliatory manner,’" Maschler said, adding that legal recourse would not be an option if that information were used to deport a DACA recipient. "They would still enjoy the opportunity to present any kind of dissent before an immigration judge."

"Precautionary discretion is used by everyone from the FBI to a local police department … but that is a manner of grace, not a right, and DACA is a matter of grace. Grace which has some regulations about it. But that does not turn it into a matter of right," she added.

But Leopold disagrees.

“ICE was not supposed to be using that information for enforcement purposes in absence of criminal convictions, fraud or a threat to national security or public safety,” Leopold said. “There is supposed to be a ‘firewall’ and I think that ICE should not be able to use that information. They could be buying themselves some serious litigation if they did.”

What About Work Authorizations?

When DACA recipients are granted status, they are separately given a work authorization.

It is unknown how the Trump administration would handle work authorizations.

“I believe that if DACA were terminated, the employment authorization documents would remain valid until the expiration dates on the cards,” Leopold said. “However, there is a regulation that provides that employment authorization may be terminated when the conditions under which it was granted change. So DACA would have to be terminated with explicit termination of employment authorization.”

So What Should DACA Recipients Do?

Immigration groups like the National Immigration Law Center recommend not applying for DACA if you do not already have it. However, if you are a DACA recipient, the government already has your information.

What steps to take depends largely on what the Trump administration does next.

"I can certainly see there being massive protests and massive pressure," Maschler said. "And see things happen that would make it decided not to [overturn DACA] for pragmatic reasons. … I think risk versus benefits comes out, if someone already disclosed information and is just renewing, they might as well renew. Someone applying for the first time, it’s a tougher call."