The Obama administration is urging dismissal of a lawsuit that would dismantle the president's immigration program, an initiative designed to spare nearly 5 million people in the U.S. illegally from deportation.

The case was brought by an Arizona sheriff, Joe Arpaio, who contends that President Barack Obama's program serves as a magnet for more illegal entries into the U.S. Arpaio says the new arrivals will commit crimes and thus burden his law enforcement resources.

In a court filing late Monday, the Justice Department told U.S. District Judge Beryl Howell that the sheriff's theory is speculative and unsubstantiated and that Arpaio has failed to show he will suffer any injury at all from the federal government's program.

The sheriff's challenge to the federal program is "meritless," the Justice Department said in its court filing.

The Justice Department said the federal program "does not grant legal status to any alien. Rather, it authorizes a temporary exercise of prosecutorial discretion on a case-by-case basis for certain individuals who have been in the United States since 2010 and have deep ties to the community."

The department said the Supreme Court has made clear that the federal government has broad discretion on immigration enforcement.

Arpaio's lawsuit was filed within hours of the Nov. 20 announcement of Obama's immigration effort. Separately, 24 states have joined in a federal court challenge in Texas alleging that Obama violated constitutional limits on presidential power. The states' lawsuit says the president's action by executive order will exacerbate the humanitarian crisis along the southern border.

Arpaio's lawsuit says Obama is "hijacking" existing immigration regulation and law, creating a radically new and different regime.

Arpaio has often clashed with the federal government over the enforcement of immigration laws and he has filed suit to stop new policies announced by Obama.

The federal initiative marks the most sweeping changes to the nation's immigration laws in nearly three decades and set off a fierce fight with Republicans.