Aside from the missing holiday pay, workers at small private companies often work long, intensive hours for low salaries, and get no social insurance or adequate protection from work hazards, workers' advocates and lawyers say.

Small, privately owned companies typically have more labor rights violations than large factories because investments or orders from foreign companies bring pressure from the overseas owners or clients to eliminate sweatshop conditions, workers' rights advocates say.

Small businesses are also less likely to come under scrutiny from the media, trade unions and law enforcement agencies.

More than 80 percent of labor disputes and most strikes are at small or medium-sized enterprises, said Zhang Mingqi, vice-chairman of the All-China Federation of Trade Unions (ACFTU), at a labor relations conference in Beijing in December.

To make matters worse, small businesses made less than a 3 percent profit from January to July because of slowing economic growth, rising labor costs and financing difficulties in China, according to the Ministry of Industry and Information Technology. The smaller companies' poor performance led to a rise in labor disputes and strikes.

To address the problem, the ACFTU is sending more than 100,000 union officials to workshops across the country to alleviate strained relations between business owners and workers, Zhang said. It has also been promoting collective bargaining systems and the establishment of trade unions.

China adopted a series of measures to improve labor protection and workers' quality of life.

Labor contracts were signed among 97 percent of all enterprises, and 65 percent of small enterprises as of 2010, according to the latest figures released by China's Information Office of the State Council in July.

In 2009 and 2010, the State investigated and dealt with 819,000 cases of violations of workers' rights in which employers would not sign labor contracts, pay salaries promptly, or participate in social insurance programs in accordance with the law.

In those two years, 2 million illegal acts were investigated and dealt with, 33,400 companies and projects that engaged in illegal production and operation were closed or canceled, and 13.6 million workplace safety hazards were eliminated.

More than 95 percent of workers in the city had signed collective contracts as of 2011, while petitions filed for labor disputes plunged 33 percent over the previous year, showed statistics from the Shenyang Federation of Trade Unions.

But significant problems remain. China saw an increasing number of labor disputes in recent years. ACFTU figures showed that mediation organizations received 406,000 labor dispute cases across the country in 2010, a 12.1 percent year-on-year rise.

Late last year, thousands of workers walked out at an LG Display factory in Nanjing to protest shrinking year-end bonuses. The company ended up paying workers a bonus equal to two times their monthly pay.