A proposed California wealth tax has yet to appear on the ballot, but it is already causing a stir among the state’s richest residents. In a bid to protect their fortunes, several billionaires are acquiring luxury properties in Miami, shifting both their lifestyles and investments eastward.

California’s proposed one-time 5 percent tax on billionaires aims to boost revenue, but skeptics warn it could open the door to far-reaching wealth taxation. With federal precedents looming, some worry that once in place, the measure might extend well beyond those at the very top.