"The next terrorist attack will come from right here", predicts American Border Patrol (ABP) founder Glenn Spencer, gesturing at the US/Mexican border. With its official sounding name, unmanned satellite planes and heat seeking imaging systems, ABP seems like a government body. But by his own admission, many of this citizen militia's actions "embarrass" the government. They've turned border control into a major political issue.

Citizen militias can no longer be dismissed as a fringe movement. Over 7,000 volunteers patrol the border, using commando techniques inspired by the Special Forces. These patriots may be heavily armed but - according to one member - it's they who are vulnerable. "The illegals can sometimes come in groups of 150. They may go ahead and start shooting at you with AK47s."

Militias believe that illegal immigrants pose a danger to national security. "Any terrorist can come in here, anytime they want", states one militia member. They claim members have found Arabic diaries and prayer mats, proving; "Arabs are coming into the country." But this is disputed by the people smugglers. "I've been doing this job for ten years and I've never, never worked with a guy who looked like an Arab".

The unpalatable truth is that the American economy relies on illegal workers. "We are the undesirables but they need us", laments Carlos Marentes. It's believed that 80% of all agricultural workers are undocumented. In Phoenix, there is a tacit recognition of this. The council approves an employment centre for illegal immigrants. "When we work through the employment centre, they note employers registration plates. If he doesn't pay, then the centre calls the police", explains Manuel.

But life is getting harder for illegal workers. "I go to restaurants and see all those illegal aliens and I'm afraid of all the diseases they transmit", states Carmen Mercer. Migrants are blamed for depressing wages and stealing American jobs. A series of emotive television adverts plays on these fears, depicting families impoverished by immigration. In them, a woman laments; "If immigration increases, we'll have more foreign workers who work for next to nothing. Mr President, I need to make enough money to feed my family."

The adverts are another sign of how the anti-immigration lobby is seizing the political incentive. "Never before have these organisations been perceived as so mainstream," states Max Blumenthal from The National. "There's a big failure on the part of government to do anything meaningful with immigration reform so you leave a vacuum which is filled by the extreme voices", explains Congressmen Raul Grijalva. As well as providing funding for approved politicians, the militias have started fielding their own candidates.

But although their actions are making it harder for migrants to cross the border, they're not putting anyone off. As one man confides: "It's very tough for us. All of us are scared but we have to go because in Mexico, we can't make a living."