Emma de Paz was selling breakfast to day laborers outside a Los Angeles Home Depot on June 19 when immigration agents showed up. Some of them chased workers through the parking lot. Others rounded up the food cart vendors. De Paz was handcuffed, forced onto her knees, and driven to a federal detention center downtown.She called her brother, Carlos Barrera, from the facility."They didn't ask if she had papers or not. They just grabbed her and put her into one of the vans," Barrera said, recalling his conversation with his sister, who has since been transferred to a desert detention center 90 miles away. "They had no reason to arrest her. They didn't have a warrant."Though his sister is undocumented, Barrera said the agents could not have known that before detaining her or many of the 29 other people they rounded up that morning."She has dark skin. They assumed she was Hispanic, and they took her," he said. "It's the racial factor.""Open season" on immigrantsImmigrant advocates and civil rights lawyers say evidence is mounting that immigration agents carrying out the Trump administration's deportation crackdown in southern California are engaging in widespread racial profiling.They've raided known hubs for Latino workers almost daily – hardware store parking lots, car washes, and street vendor corners. Videos of many of those operations, filmed by bystanders and posted to social media, have shown agents arresting people who appear to be Latino as they stand on sidewalks or wait at bus stops.On Wednesday, the American Civil Liberties Union and other legal groups filed a federal class action lawsuit alleging that immigration agents roving the streets are targeting people based on the color of their skin or their apparent occupation. They want a judge to declare the raids unconstitutional."There is a real sense that it is open season on anyone who appears to be an immigrant," said Eva Bitran, director of immigrants' rights at the ACLU of Southern California. "They are arriving, corralling people before asking one single question, just based on their location and their appearance. Often they are handcuffing people even before they have asked for their papers, or even after a person has said 'I am a US citizen, I have a green card, I have every right to be here.' "Tricia McLaughlin, assistant secretary for public affairs with the Department of Homeland Security, denied that immigration agents are engaging in racial profiling."Any claims that individuals have been 'targeted' by law enforcement because of their skin color are disgusting and categorically FALSE," McLaughlin said in a statement."DHS enforcement operations are highly targeted, and officers do their due diligence," she added. "We know who we are targeting ahead of time. If and when we do encounter individuals subject to arrest, our law enforcement is trained to ask a series of well-determined questions to determine status and removability."Rules govern immigration stopsBut some legal experts say the indiscriminate sweeps agents appear to be carrying out likely violate rules governing their authority to arrest people they encounter in public, including Fourth Amendment protections against unreasonable seizure.Under federal law, immigration agents can question anyone about their immigration status.But before arresting someone in public without a warrant, "agents have to have a 'reasonable suspicion' that someone is in the country illegally," said Jean Reisz, professor of immigration law at the University of Southern California. "That reasonable suspicion has to be based on articulable facts. It can't just be based on race. It can't be that this person looks like what I think someone from another country looks like."People are free not to answer an immigration agent's questions, but if they try to run, agents often consider that suspicious enough to arrest them, she said.Advocates say the Trump administration's ambitious daily arrest quotas are leading immigration agents to lean on the thinnest of justifications and on false assumptions about people they encounter to justify arrests."If you're asking these law enforcement agencies to arrest 3,000 people a day, they cannot form reasonable suspicion for each specific person," Bitran said. "So they have to be cutting corners."Earlier this year, the ACLU convinced a federal judge in Central California that Border Patrol agents there violated the Constitution when they carried out raids that swept up dozens of people based largely, the group said, on their Latino appearance. Those swept up included U.S. citizens."I'm a U.S. citizen!"On June 12th, Javier Ramirez was at his uncle's auto junkyard in the mostly Latino city of Montebello, east of Los Angeles, when a white unmarked SUV pulled up to the front gate. Video from a security camera shows three U.S. Border Patrol agents quickly get out, pull up their face coverings, and walk through the gate.In a second video filmed by Ramirez's brother minutes later, Ramirez is handcuffed while an agent pins him against the fence."We're all U.S. citizens!" Ramirez shouts. "I've got my passport!"He tussles with the officer, who pushes him to the ground. Agents then load Ramirez into a van and drive off."You can't take him! You can't take him!," Ramirez's brother, Abimael Dominguez, shouts.According to court filings, Ramirez was taken to the federal detention center in downtown Los Angeles. Agents confirmed his U.S. citizenship, but charged him with assaulting, resisting or impeding a federal officer.Standing outside the junkyard on a recent morning, Dominguez said that agents had no reason to suspect his brother or anyone else working there was in the country illegally."There's a lot of Hispanic brothers right here," but everyone working in the yard that day was a U.S. citizen, he said. "Racial profiling is the way I look at it. Because they just walked in and said 'hey, you and you.' "Another U.S. citizen who was temporarily detained during the raid is now a plaintiff in the ACLU's lawsuit.Javier Ramirez has since been released on bail. But his brother said he fears leaving home."He's traumatized," Dominguez said. "That sucks, to be a U.S. citizen and not be able to walk in the country of freedom. It sucks that we're antagonized for being Hispanic." Transcript AILSA CHANG, HOST: The ACLU sued the Trump administration this week, alleging that federal immigration agents roving the streets of Southern California are picking people up for deportation based on the color of their skin. Fears that the government is racially profiling are growing, as agents continue to target street vendors, day laborers, carwash workers, even people just out for walks. NPR's Adrian Florido reports.ADRIAN FLORIDO, BYLINE: Immigration agents arrested Emma de Paz on June 19, when they showed up at a Los Angeles Home Depot and began chasing day laborers through the parking lot. She had been selling breakfast to those workers from a food cart on the sidewalk. She later called her brother, Carlos Barrera, from the federal detention center. Here's what he says she told him.CARLOS BARRERA: (Speaking Spanish).FLORIDO: "They handcuffed her, forced her onto her knees and pointed a gun at her," Barrera says. His sister is undocumented, but he says the agents could not have known that. They didn't ask if she had papers. They didn't ask her any questions.BARRERA: (Speaking Spanish).FLORIDO: "They simply grabbed her and loaded her into the van," Barrera says. He and his sister are from Guatemala. They're dark-skinned.BARRERA: (Speaking Spanish).FLORIDO: "They assumed she was Hispanic, and that's why they took her," he says. His sister is still detained. Since early June, ICE and Border Patrol agents have been carrying out surprise raids all across Southern California, often in public places. In a federal lawsuit this week, the ACLU and other legal groups said agents patrolling the streets are engaged in widespread racial profiling. ACLU lawyer Mohammad Tajsar spoke at a press conference announcing the suit.(SOUNDBITE OF ARCHIVED RECORDING)MOHAMMAD TAJSAR: To them, if you are brown, they will hunt you down. To them, if you have dark skin, they will take you in.FLORIDO: Many recent immigration sweeps have been filmed by bystanders. The videos show masked agents descending on individuals or groups of people out in public. They appear overwhelmingly to be working-class Latinos.EVA BITRAN: There is a real sense that it is open season on anyone who appears to be an immigrant.FLORIDO: Eva Bitran is director of immigrants' rights at the ACLU of Southern California.BITRAN: They are arriving, corralling people before asking one single question, just based on their location and their appearance. Often they are handcuffing and putting in vans people even before they have asked for their papers. Or even after a person has said, I am a U.S. citizen, or I have a green card, I have every right to be here.FLORIDO: She hopes the judge hearing the ACLU's suit will find agents are acting unlawfully and order them to stop. Jean Reisz is professor of immigration law at the University of Southern California.JEAN REISZ: I suspect that there is a lot of illegality going on.FLORIDO: Under federal law, immigration agents can arrest someone in public without a warrant, but they have to first have reasonable suspicion that they're in the country illegally. But Reisz says...REISZ: Reasonable suspicion has to be based on what's called articulable facts, so it can't just be based on race. It can't be, this person looked like what I think someone from another country looks like.FLORIDO: In a statement to NPR, Tricia McLaughlin, with the Department of Homeland Security, denied that agents are targeting people based on the color of their skin. DHS enforcement operations are highly targeted and officers do their due diligence, she said, adding, we know who we are targeting ahead of time. Lawyers and advocates say those claims are undermined by the videos of people being picked off the streets, seemingly at random...(SOUNDBITE OF ARCHIVED RECORDING)UNIDENTIFIED PERSON #1: He's an American citizen, bro. Come on.FLORIDO: ...And by the fact that even U.S. citizens are being detained. People like Javier Ramirez - on June 12, Border Patrol agents walked into a junkyard east of Los Angeles and handcuffed Ramirez and other men working there. His brother, Abimael Dominguez, filmed his arrest on his cell phone.(SOUNDBITE OF ARCHIVED RECORDING)UNIDENTIFIED PERSON #2: He's a USA citizen.UNIDENTIFIED PERSON #3: Yeah, he's a U.S. citizen, bro.UNIDENTIFIED PERSON #4: We're all U.S citizens, all U.S. citizens. Look what you guys are doing.FLORIDO: Ramirez tussles with an agent who has him pinned against a fence. The agent pushes him to the ground. Agents then load him into a van. Dominguez, still filming, runs after it.(SOUNDBITE OF ARCHIVED RECORDING)ABIMAEL DOMINGUEZ: They're hostaging my brother. Hey, you can't take him. You can't take him. You can't take him.FLORIDO: I recently met Dominguez outside the junkyard.DOMINGUEZ: We're Americans. You're not targeting undocumented people, brother. Are you just racial profiling? - because if you're telling - if somebody's telling you, I'm an American, I got my passport in my wallet, you release the guy. Let him go.FLORIDO: According to court papers, agents took Ramirez to a downtown LA detention center. They verified that he was a U.S. citizen. They also charged him with assaulting, resisting or impeding a federal officer. He was released on bail, but his brother says he's traumatized and doesn't want to leave his house.DOMINGUEZ: You know, that sucks. That sucks to be a U.S. citizen and not be able to walk in the country of freedom, you know? It sucks. They were antagonized for being Hispanic, you know?FLORIDO: An LA federal judge has scheduled the first hearing to consider the ACLU's racial profiling claims against the government next week. Adrian Florido, NPR News.