Fortune, Jan 27 - In New York City, Mayor Bill de Blasio in a news conference said his chief legal officer would be in court the "hour" after any specific action to withhold money came through.
"There is less here than meets the eye. This executive order is written in a very vague fashion," said de Blasio, a Democrat.
San Francisco City Attorney Dennis Herrera, also a Democrat, said his office was still examining whether it could sue before Trump made any specific move to cut funds.
Trump's order directed that funding be slashed to all jurisdictions that refuse to comply with a statute that requires local governments to share information with immigration authorities.
Omar Jadwat, director of the American Civil Liberties Union's Immigrants' Rights Project, said the cities can argue "they are fully in compliance with that statute," since they do share information with federal authorities, but offer limited cooperation when it comes to turning over immigrants who are not convicted criminals.
There could also be procedural snarls to implementing the cuts, lawyers who specialize in federal grants said. If the U.S. government seeks to cut off grants to a certain recipient, it must go through a complicated process known as "suspension and debarment," and cities would have the right to appeal.
"It's fair to say that they don't understand the scope and reach of federal grants law," said Edward Waters, who heads the federal grants practice at the law firm Feldesman Tucker Leifer Fidell in Washington, referring to the Trump administration.
The White House would also have to negotiate with states that are home to sanctuary cities. Nearly 90% of $652 billion the federal government handed out through more 1,500 separate grant programs in the most recent fiscal year went to states, not directly to cities, according to a Reuters review of federal spending data.
If the Trump administration wanted to try to cut off Medicaid money to Chicago, for example, it would have to work through the state government of Illinois, which could pose an additional barrier, Waters said.
Advocacy groups for immigrants' rights said they are also preparing their own legal challenges to other aspects of two executive orders Trump signed on Wednesday, examining sections that deal with expanding detention of immigrants and changing how asylum requests are processed.