SAN DIEGO (Border Report) -- More than 240 political leaders in so-called "sanctuary municipalities" received letters last month threatening them with legal prosecution and up to 20 years in prison if they hinder mass deportations. The letters were sent out by a group called American First Legal, a firm started by Stephen Miller, Donald's Trumps next deputy chief of staff for policy. America First puts ‘sanctuary jurisdictions’ on notice In California, state Attorney General Rob Bonta got one, as well as the mayor of Los Angeles and the city's chief of police. San Diego's former Board of Supervisor's Chair Nora Vargas also received one. Many others including the mayors in big cities like Chicago, Washington D.C., and New York got one, as did small-town mayors like Las Cruces' Eric Enriquez. AFL-Sanctuary-City-LettersDownload In short, the letters issue threats saying, "your jurisdictions' sanctuary policies could expose you and your subordinates to criminal liability for conspiracy to commit a federal offense and conspiracy to impede a federal officer." To improve border security, asylum processes, US must take these steps, group says Those who received the letters are told they could face "up to 20 years imprisonment." "The threat of criminal prosecution is really not realistic,” said Robert Shapiro, dean of the University of San Diego's School of Law. Maquiladora sites to help Mexican border town shelter deported migrants Border Report asked Shapiro to review the letters from a legal and independent perspective. Robert Shapiro is the Dean at the University of Diego's Law School. (Salvador Rivera, Border Report) "That letter that was sent out threatens criminal prosecution and things like that, I suppose if state and local officials were actively obstructing what federal officials were doing, there could be those kinds of legal sanctions," said Shapiro. "In general, when California or other states or other cities talk about being sanctuary jurisdictions, they don’t mean they’re actually going to blockade what federal officials are doing, what they mean is they’re not going to assist." According to Shapiro, not helping or not wanting to help, is not a crime. US ‘knowingly killing migrants,’ county official says "They’re not going to give information to federal authorities, they're not going to enforce the federal law themselves and in general that’s perfectly legal." Shapiro expects very little, if any prosecutions at all. "This really is just a replay of what went on during the first Trump administration, there were no criminal prosecutions of state local officials in that administration and assuming state and local officials do what they did at that time, there won’t be any criminal prosecutions this time either." Rising US-Mexico tension a game of optics, analyst says Border Report reached out to several recipients of the letters seeking comment. Only Bonta, California's Attorney General responded. In a statement, his spokesperson called the letters "a scare tactic plain and simple." "While we are unable to comment on the specifics of the letter, we want to be clear: SB 54 was upheld by the courts during the first Trump administration, and it prevents the use of state and local resources for federal immigration enforcement with certain narrow exceptions. SB 54 does nothing, however, to block federal agencies from conducting immigration enforcement themselves. California will continue to comply with all applicable state and federal laws, and we expect all local law enforcement agencies to do the same." President-elect Trump has said mass deportations are necessary as a way to make the United States a safer country. Visit the BorderReport.com homepage for the latest exclusive stories and breaking news about issues along the U.S.-Mexico border Many migrant advocates, including the American Civil Liberties Union, say mass deportations will decimate American communities by targeting immigrants who are already contributing members of society while leading to countless family separations.