Immigration and Nationality Act

This is what I found on the U.S. Citizenship and Immigration Services (USCIS) web site at:
http://www.uscis.gov/ilink/docView/SLB/HTML/SLB/0-0-0-1/0-0-0-29.html

IMMIGRATION AND NATIONALITY ACT
Sec. 264. [8 U.S.C. 1304]

(d) Every alien in the United States who has been registered and fingerprinted under the provisions of the Alien Registration Act, 1940, or under the provisions of this Act shall be issued a certificate of alien registration or an alien registration receipt card in such form and manner and at such time as shall be prescribed under regulations issued by the Attorney General.

(e) Every alien, eighteen years of age and over, shall at all times carry with him and have in his personal possession any certificate of alien registration or alien registration receipt card issued to him pursuant to subsection (d). Any alien who fails to comply with the provisions of this subsection shall be guilty of a misdemeanor and shall upon conviction for each offense be fined not to exceed $100 or be imprisoned not more than thirty days, or both.

 Also
Immigration and Customs Enforcement (ICE) Enforcement Activities: Common Questions
http://www.lawhelp.org/documents/1974518106EN.pdf?
Source: Northwest Justice Project

I am a lawful permanent resident and must carry my green card. Can I be arrested if I refuse to produce it when ICE asks me for it?
The law requires that everyone over 18 to carry their alien registration card. Failure to carry it constitutes a misdemeanor. However, since the Fourth Amendment requires that government officers must have a reasonable suspicion of illegal activity before they detain someone, the ICE does not have the authority to force an alien to produce evidence of registration unless it has a reason to believe that he or she will be unable to do so.

What is a "detention?"
A "detention" or a "seizure" occurs under the fourth amendment when that person yields to any official show of authority or physical force. For example, if five ICE officers surround you at
your workplace, tell you that you cannot go back to work until you have answered their questions, you have probably been "detained," or "seized." If ICE officers stop your car, you have been "detained." If one officer casually comes up to you and asks to see your papers, you have probably not been "detained."

What kind of proof does ICE have to have to "detain" me?
ICE may not detain you unless the officer has a "reasonable suspicion" that you are an undocumented alien.

Under what circumstances can ICE stop my car?
An ICE stop of a car is a "detention." Therefore, ICE may stop a car only if the officers have a reasonable suspicion that undocumented aliens are in the car.

What is a "reasonable suspicion?"
A reasonable suspicion is a standard less than probable cause. It means facts that would lead the officer to believe there are undocumented aliens present. The officer may not base a stop of a car or detention of a person on a "hunch," or solely on the driver's or occupants' ethnic appearance or name. Therefore they cannot detain you or stop your car solely because you look like a Hispanic person.

However, ICE may base a suspicion of illegal alienage on a combinations of factors, which may include attempts to avoid Border Patrol agents, location with respect to the border, tips that undocumented workers are in the area, speech, manner of dress, presence in a vehicle commonly used for smuggling across the border, and prior presence of undocumented workers in the area or employment.

and this page 
http://www.uscis.gov/portal/site/uscis/menuitem.eb1d4c2a3e5b9ac89243c6a7543f6d1a/?vgnextoid=d0a33a4107083210VgnVCM100000082ca60aRCRD&vgnextchannel=d0a33a4107083210VgnVCM100000082ca60aRCRD

What The Law SaysSection 264 of the Immigration and Nationality Act (INA) states, "Every alien in the United States . . . shall be issued a certificate of alien registration or an alien registration receipt card in such form and manner and at such time as shall be prescribed under regulations . . ." It also says, "Every alien, eighteen years of age and over, shall at all times carry with him and have in his personal possession any certificate of alien registration or alien registration receipt card issued to him . . .. Any alien who fails to comply with [these provisions] shall be guilty of a misdemeanor..." The specific requirements and procedures for applying to renew an expiring green card are contained in the Code of Federal Regulations [CFR] at 8 CFR section 264.5.