Donald Trump's incoming "border tsar", Tom Homan, has vowed to slash federal funding to states that do not cooperate with the administration's promises of mass deportations of undocumented migrants.
Several states, including California, Illinois, New Mexico and Arizona have vowed to push back against Trump's plans, and legal challenges are a near-certainty.
Trump has said he plans to use the use the US military to conduct the deportations, and Homan has said he "guarantees" that federal funding can be wielded as a tool against jurisdictions that stand in the way.
There are at least 13 million undocumented immigrants living in the US.