State troopers are joining the domestic front in the war on terror.

Since September of last year, state police have had the authority to arrest and detain illegal immigrants and hand them over to federal authorities for possible deportation. Alabama is among the first states to help.

"We went through an entire series of document training," explained Gary Hetzel, one of 21 Alabama state troopers trained to enforce immigration laws. "So we can tell if [a document's] been altered, if it's an actual visa or, with the LPR cards, if it's fake."

Lawful permanent residence, or LPR, cards are more commonly known as "green cards."

Homeland Security officials welcome the police assistance, but some immigrant rights groups are skeptical.

"The concern [is] that people are going to go outside of the general duties that they've been given and use racial profiling (search)," said Isabel Rubio of the Hispanic Interest Coalition (search).

To prevent profiling, state troopers are permitted to enforce immigration rules only in connection to traffic violations.

So far, Alabama and Florida are the only states to partner troopers with the Department of Homeland Security (search). But others are expected to follow as federal, state and local authorities attempt to maximize resources in the domestic war on terror.

Click here to watch a report by Fox News' Jonathan Serrie.