On a recent eight-hour shift at a McDonald’s in Hong Kong, Luke Ching, 52, wiped tables, cleared trays of half-eaten fries, emptied cups of soda and milk tea and lugged bulging trash bags to the dumpster.

For him, the main goal of the part-time work was not making ends meet. It was research for his main pursuit: using art to advocate for better treatment of people in menial jobs in a city with one of the widest income gaps in the world.

That project came to an abrupt end last month when he was fired after publicly calling on McDonald’s Hong Kong to reinstate paid meal breaks for employees at its local outlets. Undeterred, Mr. Ching is pushing ahead — even as the scope for broader political protest has shrunk in the city.

“Many people have accepted that they’re not allowed to speak critically about their workplace. But employees don’t exist just to drive profit,” Mr. Ching said in an interview. “We have the right to express ourselves in public.”

Over the past two decades, his campaigns have cut across the worlds of art and activism, gaining him a wide following of supporters as well as some online detractors, who call him attention-seeking and gimmicky.