Federal Law
8 USC Sec 1325 - Illegal Entry
Any alien who enters U.S. other than at A port of entry by false or misleading representation shall be subject to civil and criminal penalties can be fined and imprisoned

Section 1324a  Hiring - Harboring - Transporting any illegal alien
Any person who knowingly hires/harbors/ transports any illegal alien is guilty of a felony punishable by 10 years jail + $2,000 fine per illegal alien + forfeiture of vehicle or property used to commit the crime.
 
Section 1324c  Law officers have authority to make arrests...
All officers whose duty it is to enforce criminal laws shall have authority to make arrests for violation of any provision of this section (affirmed US vs. Perez-Gonzalez 2002 Fed App 0360, 6th Circ.) Section 1324a Hiring - Harboring - Transporting any illegal alien.

Section 1644
No local ordinance, rule, or measure shall stop law enforcement officers from enforcement of this section (affirmed Southern District Court of NY, US vs. Rudy Giuliani, 1996.