Mostly Ballroom dancing around Federal Immigration laws already on the books. Each one of these Mayors could and should be arrested and convicted for Federal Crimes. The hope is that this show is a precursor to Trump stopping ALL Federal Aid to these cities and States.
The only highlight so far is Anna Paulina Luna who just said she's referring each of these mayors to the Justice Department for prosecution.
8 USC 1324: Bringing in and harboring certain aliens
https://uscode.house.gov/view.xhtml?req=granuleid:USC-prelim-title8-section1324&num=0&edition=prelim