China's top trade union organization will prioritize setting up unions in all overseas-funded businesses that have been operating in the country for more than five years, particularly the world's four-biggest audit firms, which have a strong presence in China.

Of the roughly 200,000 foreign-funded corporations in China, 91.4 percent had union representative by the end of 2012, said Wang Ying, a deputy chief overseeing grassroots labor organizations in the All-China Federation of Trade Unions.

"There are still enterprises that have invested in China for many years but are still reluctant to set up unions," she said, highlighting particularly the 'Big Four' audit companies of PricewaterhouseCoopers, Deloitte Touche Tohmatsu Ltd, Ernst & Young, and KPMG, which together employ nearly 40,000 people nationwide.