SHANGHAI—A campaign calling on workers at Chinese tech companies and other high-profile firms to log their working hours on a public internet page has gone viral, in the latest backlash against a culture of overtime. Organized by four anonymous creators who described themselves as recent graduates, the “Worker Lives Matter” campaign calls on employees at tech firms to enter their company name, position, and working hours in a spreadsheet posted on GitHub. As of Thursday morning, more than 4,000 people who said they worked at tech giants such as Alibaba Group Holding Ltd., Baidu Inc., Tencent Holdings Ltd., and ByteDance had registered their data. Employees have since also created separate spreadsheets for specific sectors such as real estate, finance, and foreign companies. A majority of the entries on the spreadsheet show that while a five-day week is the norm, many staffers work 10 to 12 hours a day. One of …