Immigration agents are not required to obtain warrants to detain suspects. The agents also have broad authority to question people about their immigration status and to search them and their homes. There are no Miranda rights that agents must read when making arrests. Detained immigrants have the right to a lawyer, but only one they can pay for.
No Need for a Warrant, You’re an Immigrant
http://www.nytimes.com/2007/10/14/weekinreview/14preston.html
No Need for a Warrant, You’re an Immigrant
http://www.nytimes.com/2007/10/14/weekinreview/14preston.html