Much of the discontent stems from a new scheduling system that Walmart put in place this summer as a way, the company said, of giving workers more flexibility. Workers have argued that it has resulted in cuts to overtime pay and excessively long shifts, and some say they were coerced into signing new contracts agreeing to the system.

Walmart denied that it had treated its employees unfairly or had pressured them to accept the new schedules. Rebecca Lui, a spokeswoman, said that the vast majority of its work force supported the new system, and that employees were free to keep their old schedules.

“Our associates are our most valuable asset,” she said in a statement.

Zhai Xiuhua, a former greeter at a Walmart store in Shenzhen, said she was fired in September after leading a fight against the new scheduling system.

“I told them, ‘Even if you put a knife to my neck, I’ll never agree,’” she recalled at her home, where her uniform and identification badge — No. 14470 — still hang on the wall. Ms. Zhai, worried about medical bills, says she now hopes to find work in her hometown in the southwestern province of Sichuan.

Walmart, which has resisted unionization at its thousands of stores across the world, was forced by the government in 2006 to establish branches of the Communist Party-controlled All-China Federation of Trade Unions for its roughly 100,000 Chinese employees, part of a broader push by the party to unionize foreign businesses.

But union branches at many Walmart stores are under the thumb of store managers, and higher-level union officials appear torn about how to respond to complaints from workers like Ms. Zhai.