Amid the Trump administration's ongoing crackdown on illegal immigration, the nation's immigration service is warning immigrants to carry their green card or visa at all times. U.S. Citizenship and Immigration Services posted the reminder July 23 on social media: "Always carry your alien registration documentation. Not having these when stopped by federal law enforcement can lead to a misdemeanor and fines." Here's what immigrants – and American citizens – need to know. The law requiring lawful immigrants and foreign visitors to carry their immigration documents has been on the books for decades, dating to the 1950s. The Immigration and Nationality Act states: "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." But the law had rarely been imposed before the Trump administration announced earlier this year that it would strictly enforce it. The "carry your papers" portion fell out of use for cultural and historical reasons, said Michelle Lapointe, legal director of the nonprofit American Immigration Council. In contrast to the Soviet bloc at the time the requirement was written, "We have never been a country where you have to produce evidence of citizenship on demand from law enforcement." In a "Know Your Rights" presentation, the ACLU cautions immigrants over age 18 to follow the law and "carry your papers with you at all times." "If you don't have them," the ACLU says, "tell the officer that you want to remain silent, or that you want to consult a lawyer before answering any questions." Many immigrants preferred to hold their green card or visa in safe-keeping, because, like a passport, they are expensive and difficult to obtain. Historically, it was "a little risky for people to carry these precious documents such as green card, because there is a hefty fee to replace it and they are at risk of not having proof of status – a precarious position to be in," Lapointe said. But as immigration enforcement has ramped up, the risks of not carrying legal documents have grown. Failure to comply with the law can result in a $100 fine, or imprisonment of up to 30 days. 🚨 Attention 🚨Always carry your alien registration documentation. Not having these when stopped by federal law enforcement can lead to a misdemeanor and fines.pic.twitter.com/WAmOeQtLjP — CBP (@CBP)July 23, 2025 U.S. citizens aren't required to carry documents that prove their citizenship. But in an environment of increasing immigration enforcement, Fernando Garcia, executive director of the nonprofit Border Network for Human Rights in El Paso, Texas, said he worries about U.S. citizens being targeted. "With massive raids and mass deportation, this takes a new dimension," he said. "How rapidly are we transitioning into a 'show me your papers' state?" "The problem is there are a lot of people – Mexicans, or Central Americans – who are U.S. citizens who don't have to carry anything, but they have the burden of proof based on racial profiling," he said. "There are examples of U.S. citizens being arrested already, based on their appearance and their race." Not just immigrants:Why some Native American citizens worry about getting caught in ICE's net The Trump administration's widening immigration crackdown has already netted American citizens. In July, 18-year-old Kenny Laynez, an American citizen,was detained for six hoursby Florida Highway Patrol and Border Patrol agents. He was later released. Federal agents alsodetained a California man, Angel Pina, despite his U.S. citizenship in July. He was later released. Elzon Limus, a 23-year-old U.S. citizen from Long Island, New York, decriedhis arrest by ICE agentsin June, after he was released. In a video of the arrest, immigration agents demand Limus show ID, with one explaining he "looks like somebody we are looking for." In updated guidance, attorneys at the firm of Masuda, Funai, Eifert & Mitchell, which has offices in Chicago, Detroit and Los Angeles, advise U.S. who are concerned about being stopped and questioned "to carry a U.S. passport card or a copy of their U.S. passport as evidence of U.S. citizenship." Lauren Villagran can be reached at lvillagran@usatoday.com. This article originally appeared on USA TODAY:'Carry your papers' law: What immigrants need to know