The U.S. Constitution grants the federal government supreme authority to regulate naturalization, immigration and foreign policy. So it should surprise no one, least of all Utah legislators, that the federal government has filed suit to invalidate this state's new immigration enforcement law. Many critics argued from the inception of the Utah law that it was unconstitutional. The federal courts are likely to agree.
The basic reason for that is plain. The nation cannot have a patchwork system of different immigration laws and policies in the 50 states. That would lead to haphazard enforcement and undermine U.S. foreign policy. Other nations are not likely to take kindly to having the treatment of their citizens in the United States left to the random whim of politicians in Salt Lake City or Phoenix or Montgomery.
Despite that, Utah lawmakers plunged ahead, the bit of the immigration controversy clenched firmly in their teeth. This is unlikely to change policy the Utah law probably is invalid but it makes a lot of expensive work for lawyers.