(NewsNation) — New details are emerging about how the next administration will deliver on President-elect Donald Trump’s campaign promise to deport millions of people who crossed into the country illegally.

Trump’s transition team is already looking into the logistics and reportedly considering a major boost to surveillance for immigrants, including the use of ankle and wrist monitors.

The goal is to alleviate the stress on local jails, which have been used to detain immigrants but have struggled with overcrowding. At times, detainees have been forced to sleep on the floor, Martin County, Florida, Sheriff William Snyder told NewsNation.

“My jail is overcrowded right now and 50% of the people are sleeping on the floor in my jail because I don’t have adequate bed space,” he said. “[It’s] taken up by undocumented and illegal immigrants.”

Trump’s plan is already being met with pushback from critics and Democratic mayors of major cities, with Denver, San Diego and Chicago reaffirming their status as sanctuary cities.

And, some members of Congress are already vowing to fight such efforts.

“I think some of these mayors and governors who say they will remain sanctuary cities and states, they’re going to find themselves in hot water with hopefully Attorney General Pam Bondi as she looks into obstruction of justice and aiding and abetting criminal cartels,” said Rep. Andy Biggs, R-Ariz.

Biggs believes sanctuary cities and jurisdictions pose one of the largest obstacles to the incoming administration and Congress when it comes to the deportaiton plans. It’s estimated that millions of immigrants who entered the country illegally have found residence in sanctuary communities, but the Trump administration says it is ready to tackle that challenge.

Trump has vowed to put deportation operations into place quickly and the expansion of some tools such as ankle monitors is one possible tactic to avoid overcrowded jails.

Immigration and Customs Enforcement has been making the case for years that tools such as ankle monitors will bring down costs, with an estimate that they would cost on average $8 a day compared to $150 daily to detain someone.

On the other hand, the American Bar Association has opposed such surveillance techniques, calling them punitive and over-encompassing because they are employed without selective assessment of individual cases.