The first time Sun Heng performed his number, he knew he could start a movement. His amphitheater was a construction site in Tianjin and his audience hundreds of tired workers from villages across China: "the masses." Sun thumped his guitar strings and sang in his loudest voice, "Unite your hearts and strive as one/ And get your money when the work is done." The song, Unite for the Money, resonated with the migrants. The boss owed everyone back pay, and they knew he might leave them penniless in a strange city. The foreman, who had thought Sun might lighten the May 1 International Labor Day holiday with some folksy ditties, was livid. To show his willingness to pay salaries, he stood in front of everybody and offered Sun money. Sun refused. "He didn't need to pay me," Sun says, "just the workers."

It's not quite yet a movement, but through his music for migrants Sun wants to help organize the roughly 120 million Chinese who have moved to cities in the past decade looking for work. Most male migrants come from poor villages and work on dangerous construction sites. Urbanites disdain them as bumpkins, and most governments deny them services like subsidized medical care and public schooling for their kids. They're similar to the desperate American farmers who fled the dustbowl, heading for California in the 1930s. But whereas the sagas of the Okies—families fleeing Oklahoma poverty—were recounted in books like The Grapes of Wrath, the dramas experienced by today's Chinese migrants have been mostly ignored. Sun tries to rectify this. The unpaid musicians, comedians and poets in his Young Workers Art Troupe are all migrants themselves, so they know their fan base. "The government says it protects the interests of migrants, but it really doesn't," says Li Changping, a liberal editor of China Reform magazine, a government manual on the legal rights migrants should enjoy. "For a migrant to call for protecting his own interests is new."

Now 27, Sun was born in the remote mountains of northern China, where as a child he sang folk songs about the nearby Yellow River. "My biggest dream was to see past the nearest peak," he says. Sun got his wish when the family moved to Henan, one of China's poorest provinces. One of his formative experiences was working his way through teachers' training school by helping his mother sell produce from the family plot. Government officials tried to collect vending fees, and when his mother couldn't pay, they confiscated her cabbages for their own tables. "They were eating the people's vegetables," he recalls. "I thought, in the future I want to change this unfairness." After graduation Sun took to the rails, shacking up in the newly formed migrant communities. Teaching himself guitar, he turned to busking. He became the closest China has to Woody Guthrie, the Okie who hopped freight trains across America and wrote songs about migrant struggles, including This Land Is Your Land.

These days, Sun's the center of a growing network of students and researchers united in their desire to better the lot of migrant workers. Last month his troupe performed for 400 workers at a construction site in Beijing. The acts capture the discrimination migrants face. A stand-up comedian lampoons untouchable Beijing women who snicker at his accent. A poet regrets spending the Lunar New Year in a poor migrant shanty instead of in his familiar village. Before closing, Sun distributes copies of China Reform. So many workers crush forward that he has to fling copies through the air. Sun hasn't gone so far as to call for migrant-labor unions, which would land him in jail. Instead, he sees himself as a lightning rod. He plans a small library in the migrant district of Beijing to give workers a place to mingle. "In five years we'll have these troupes all over China," he says. They'll spread a welcome gospel of workers' rights.