NEW YORK/WASHINGTON (Reuters) – President-elect Donald Trump will be able to make many of his promised changes in immigration policy unilaterally by exercising the same kind of executive powers he criticized President Barack Obama for using.

But while most of the measures laid out in a ten-point immigration policy plan on Trump’s transition website could be set in motion without legislative approval, fully implementing them would require funding that Congress would have to approve, legal experts said.

Two core pieces of Trump’s plan, for example, involve removing more criminal immigrants who are in the country illegally and ending “catch and release” of those who cross the border illegally and are awaiting court hearings.

Shifting policy on both issues could be accomplished by putting out new enforcement directives to agents in the field from the Department of Homeland Security.

But the changes would be expensive, requiring a dramatic expansion of immigration courts and detention facilities used by Immigration and Customs Enforcement, said  Stephen Yale-Loehr, an immigration law expert at Cornell Law School.

More deportations would require more staff at every level of the system to investigate, apprehend and process those targeted. Immigration courts already have a backload of more than 500,000 cases. Detention space is currently stretched to house 41,000 immigrants currently awaiting deportation or hearings and far more holding facilities would be needed if detainees were no longer released while awaiting court dates.

Even then, completely ending the release of immigrants awaiting hearings would be difficult: A recent court decision has prohibited detention longer than 20 days for adults and children migrating together, a demographic that surged to more than 77,000 in fiscal year 2016.

Trump’s transition team has not explained how the new president intends to implement his plans.

“The President-elect is very focused on naming his cabinet, building out his administration and preparing to hit the ground running on Inauguration Day,” said Jason Miller, a spokesman for the Trump transition team. “There will be plenty of time to discuss detailed policy specifics after the swearing-in.”

Democratic attorneys general and civil rights groups are already busy preparing legal arguments to try to stop Trump’s executive actions should he implement some of his proposals. The pushback will be similar to the challenges Obama faced from Republican attorneys general and conservative groups when he acted alone to try to shield nearly 5 million immigrants from deportation.

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Among the easiest immigration promises for Trump to fulfill will be his vow to reverse Obama’s executive orders. The president-elect could eliminate with a pen-stroke Obama’s 2012 policy allowing immigrants brought here illegally as children to apply for work permits, a program known as DACA that Trump has said he will end.

What would happen next is unclear. More than 740,000 people have been approved for deportation relief under the program, and many worry that their addresses and other identifying information could be used by the new administration to target them for deportation.

Steve Legomsky, former chief counsel at U.S. Citizenship and Immigration Services, said no laws would prevent the Trump administration from using program records for immigration enforcement, but the president-elect has not said he would do so.

Denying visas to people from countries “where adequate screening cannot occur,” another point on Trump’s immigration plan, could also be easily accomplished by the president.

Under current law, the administration can unilaterally suspend visas for any individuals or groups of people deemed “detrimental to the interests of the United States.”

In the past, presidents have chosen to apply this statute narrowly – to keep out particular dictators or to deal with emergencies, for example. But the law is worded very broadly and could theoretically be applied to entire countries, said David Martin, emeritus professor of international law at University of Virginia School of Law.

Trump’s promise to make legal immigration better serve America and its domestic workforce would likely focus, at least initially, on temporary employment visas such as the H1-B, which are issued to specialized workers in fields such as technology.

While Congress sets the maximum number of visas that can be issued annually, Trump could ask the Department of Justice to step up investigations of companies using those visas, with a focus on whether they are discriminating against American workers. This could include banning more tech outsourcing firms, which are the largest users of H-1B visas, from the program if they violate the rules, said Ron Hira, a professor at Howard University.

“Employers are going to be caught up in the cross hairs,” said business immigration lawyer Matthew Dunn from the law firm Kramer Levin.

(Reporting by Mica Rosenberg in New York and Julia Edwards Ainsley in Washington D.C., additional reporting by Roberta Rampton; Editing by Sue Horton and Mary Milliken)

IMAGE: A young boy holds U.S. flags as immigrants and community leaders rally in front of the U.S. Supreme Court to mark the one-year anniversary of President Barack Obama’s executive orders on immigration in Washington, November 20, 2015.REUTERS/Kevin Lamarque