Aaron Hall, an immigration attorney in Aurora, Colorado, is still trying to figure out what exactly to tell his clients about a new Trump administration policy that allows federal immigration agents to quickly deport undocumented immigrants they encounter anywhere in the U.S.

For the past 15 years, the fast-track deportation process, known as expedited removal, has been used mostly by Border Patrol agents near the border. But now, for the first time, Immigration and Customs Enforcement (ICE) agents can unilaterally question, arrest, detain and deport undocumented immigrants who have been here for less than two years that they encounter anywhere in the country.

Does that mean immigrants should carry all their papers proving their legal status every time they leave the house? Should undocumented immigrants carry paperwork showing they've been in the country longer than two years? Should all Hispanics approached by ICE remain silent and demand to speak with an attorney?

"It's really tricky," Hall said. The only certainty is that "people who have legal immigration status, or have pending applications, or even U.S. citizens, will be put into expedited removal proceedings, and some will be deported before they’re able to make their case."

The nationwide expansion of expedited removal, which took effect July 23, may be one of the most consequential changes to immigration enforcement under Donald Trump's presidency.

To combat illegal immigration, the White House has focused mostly on the southern border, deploying National Guard and active-duty military troops to stem what they describe as a national security crisis. But expanding expedited removal moves immigration enforcement far from the border and into every community in the U.S.

That dramatic expansion, which has been considered since the early days of the Trump administration, has opened a wide range of questions about the way federal immigration agents will use their new powers, how to limit cases of racial profiling and how many legal residents and U.S. citizens will be caught up in the process.

"It means that the only limit on (the administration's) ability to deport brown-skinned people is going to be the number of detention beds they have," said Simon Sandoval-Moshenberg, legal director of the immigrant advocacy program at the Legal Aid Justice Center based in Charlottesville, Virginia.

ICE, which is primarily responsible for arresting undocumented immigrants in the interior of the country, said its agents do not, and will not, conduct "random or indiscriminate" raids as it expands its use of expedited removal. Instead, the agency said, it will continue using "targeted enforcement operations" to identify and arrest specific undocumented immigrants. ICE vowed to use the new powers responsibly.

"ICE's routine targeted enforcement model remains the same," spokesman Richard Rocha said. The only change is "how ICE is able to remove aliens."

Expedited removal was created by Congress in 1996. It allows federal immigration agents to bypass the regular deportation system, which includes court hearings, appeals and a final deportation order signed by a judge. The immigration agent needs only approval from a supervisor in the field, and the decision cannot be appealed in any court.

The main exception provided in the law is for undocumented immigrants who request asylum. Once the undocumented immigrant claims a fear of returning to his or her home country, the immigrant agent is supposed to pause the deportation process until an asylum officer can hear the person's claim.

At first, the program was used sparingly. President Bill Clinton allowed it to be used only against people who entered U.S. ports of entry without a visa or valid travel documents.

In 2004, President George W. Bush expanded its use to include people caught within 100 miles of the nation's land border with Canada and Mexico and people who had illegally entered the country within the previous two weeks. President Barack Obama maintained that structure.

From the first days of Trump's presidency, the administration saw expedited removal as a way to get around the historic backlog in immigration court and more quickly deport more undocumented immigrants.

Department of Homeland Security Secretary Kevin McAleenan made it official when his agency published a rule expanding expedited removal to the fullest extent allowable under law. Federal immigration agents can use expedited removal against people caught anywhere in the country who arrived within the previous two years.

McAleenan said the expansion is "one more tool" his agents could use to confront the "security and humanitarian crisis on the Southwest border."

Immigration attorneys, and even some government reports, raise serious questions about granting ICE agents powers to unilaterally deport people from the country.

One major concern is that people legally residing in the U.S. – citizens, permanent residents or visa holders – will be erroneously scooped up by federal agents.

That's what happened in June when Francisco Erwin Galicia, 17, who was born in Dallas, was arrested by Border Patrol agents. Even though his attorney said Galicia was carrying his Texas state ID and a wallet-sized copy of his birth certificate, the government held him for 26 days. It wasn't until The Dallas Morning News ran a story about his case that Galicia was released.

Such cases have been on the rise since Trump took office.

In the final year of Obama's presidency, ICE agents questioned 5,940 U.S. citizens, according to government data obtained by the American Immigration Council. In the first year of the Trump presidency, following orders that freed ICE agents to target a broader group of people, ICE agents questioned 27,540 U.S. citizens, a nearly fivefold increase.

"With this expansion of authority, we can expect that that would grow exponentially," said Royce Murray, managing director of programs at the council. "And it's unclear what if any checks and balances there will be to make sure we are not putting U.S. citizens and others at real risk."

The U.S. Commission on International Religious Freedom, a body created by Congress, has studied expedited removal for more than a decade. In its first study published in 2005, it found that an "alarming" number of Border Patrol agents violated the rules of implementing expedited removal.

In some cases, agents didn't ask if people feared returning to their home country, a legally required step. In other cases, commission observers heard undocumented immigrants request asylum, but Border Patrol agents wrote down that they had not.

In all, 15% of the undocumented immigrants who requested asylum were deported before getting an asylum hearing, the report found. The commission reviewed the program again in 2016, and even though it was given far less access to expedited removal interviews, it concluded that problems remained rampant.

There are also questions about whether the use of expedited removal in places away from the border are legal. Congress allowed that to happen, but because the Trump administration is the first to try it out, the legality of the process has never been tested.

The Congressional Research Service, a nonpartisan group that conducts research for members of Congress, found that courts have generally allowed people to be deported through expedited removal near the border. But courts raised questions about eliminating due process rights for immigrants the longer they've been in the country and the farther they are captured from the border.

That's why the nationwide use of expedited removal "remains an unresolved question," the service concluded in a report in 2018.

U.S. law makes clear that people who are deported through expedited removal cannot challenge their deportation. Even challenging their initial arrest on constitutional grounds may be impossible, as evidenced by a case filed last year.

In February 2017, ICE agents arrested nine undocumented immigrants in two separate locations in Northern Virginia, even though they were searching for different people. A group of the immigrants sued, claiming they were racially profiled and wrongly detained in violation of their Fourth and Fifth Amendment rights. A federal judge allowed the case to proceed, ruling that the undocumented immigrants raised "clear violations of a known constitutional right."

In April, a three-judge panel of the U.S. Court of Appeals for the 4th Circuit – one nominated by Trump, all three nominated by Republican presidents – struck down the lawsuit, ruling that Congress had not created any mechanism for ICE agents to be sued in federal court, meaning the case couldn't proceed.

Sandoval-Moshenberg, who represents the undocumented immigrants and appealed the court of appeals decision, said the ruling shows how helpless immigrants will be as ICE agents use their expanded powers.

"It's a shocking ruling," he said. "It drastically expands the number of people who will never even go before a judge, so they have no one."

In a statement, ICE said it does not usually approach people on the street and question them about their immigration status. But the statement points out that Congress gave ICE agents the power to do just that, quoting a section of U.S. law that allows agents to interrogate any "person believed to be an alien as to his or her right to be or remain in the United States."

The American Civil Liberties Union and the American Immigration Council filed a lawsuit challenging the nationwide expansion of expedited removal last week.

Immigrants remain in a state of apprehension, knowing that any encounter with ICE may lead to their quick removal from the country. Megan Lantz, a lawyer who represents immigrants who work in meatpacking plants and farms around Ames, Iowa, simply hopes she'll be able to talk to immigrants before they're on a plane back home.

"Immigration officers have total authority here," she said. "So there's no chance for me as a lawyer to fight for that person. That is really concerning."