When Hong Kongers held an unofficial referendum last month to call for democratic reforms, Beijing branded it as “illegal” and Chinese state media called it “mincing ludicrousness.” Now residents of Macau, China’s other special administrative region and the world’s largest center for gambling, are planning an unofficial referendum of their own.

Like Hong Kong, Macau is governed by a chief executive chosen by an election committee that critics say is largely pro-Beijing. Unlike Hong Kong, Macau has been mostly apolitical since the city’s return to Chinese control in 1999. (For instance, while a proposed national security law prompted half a million people to protest in Hong Kong in 2003, a similar law was approved easily in Macau in 2009.)

But now the Macanese, angered by growing inequality and an influx of migrants from the Chinese mainland, are becoming more politically active. In May, Macau’s chief executive withdrew a bill that would grant officials lavish retirement packages after more than 20,000 protesters…