By Aldo Gamboa
President Barack Obama's administration has formally asked the US Supreme Court to uphold measures it enacted shielding four million undocumented migrants from deportation.
Immigration has become a central issue as politicians gear up for the 2016 presidential race, especially after Republican frontrunner Donald Trump claimed that Mexico was sending drug dealers and "rapists."
The 45-page appeal filed on Friday (local time) challenges lower federal court rulings that blocked Obama's efforts to reform parts of the US immigration policy via executive order.
"The decision warrants immediate review," reads the appeal, signed by Solicitor General Donald Verrilli.
In November 2014 Obama issued decrees allowing people who illegally immigrated to the United States, but whose children are legal residents, to remain in the country while their legal status is resolved and be allowed to work.
It was an attempt to bypass Congress - where immigration reform is hopelessly stalled - by ordering government agencies to focus on deporting serious criminals, rather than undocumented immigrants who live and work in the United States.
The move was quickly blocked in court by conservatives, who argue that Obama had gone well beyond his executive powers. The governors of 26 US states, led by Texas, took up the case.
Republicans and Democrats agree that sweeping immigration reform is overdue, but bitterly disagree about how to do it.
A federal court in Texas in February ruled against the administration, as did a federal court in Louisiana in early November - putting the program on hold and prompting the current appeal.
There are nearly 12 million unauthorised immigrants living in the United States, and an estimated four million would qualify under Obama's orders.
It is unclear if the Supreme Court will resolve the case before Obama leaves office in January 2017.
The appeal says that the current injunction on the measures has a "far-reaching and irreparable humanitarian impact."
The government argues, among other things, that it has broad authority in the area of immigration.