China's top trade union announced yesterday that McDonald's, KFC and Pizza Hut have violated the country's labor laws by underpaying part-time workers in the southern city of Guangzhou.

The fast-food giants must correct their wrongdoings and pay the workers retroactively, said Li Shouzhen, a senior official with the All-China Federation of Trade Unions (ACFTU).

"A joint investigation by the Guangdong provincial trade union and the labor authorities confirmed media reports about the companies' unlawful practice," Li told a news briefing in Beijing.

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"The federation will uncompromisingly fight any practice that violates workers' rights," he added.

Li said the ACFTU had instructed its Guangdong branch to negotiate with the companies on behalf of the 3,000-odd part-time workers, most of them college students.

The case was brought to public attention by local newspaper New Express, which said McDonald's, KFC and Pizza Hut in the capital of Guangdong Province were paying part-time workers up to 40 percent less than the minimum wage.

The southern metropolis set the minimum wage at 7.5 yuan (97 cents) per hour for part-time workers at the beginning of this year. But McDonald's pays only 4 yuan (52 cents), KFC 4.7 yuan (61 cents) and Pizza Hut 5 yuan (65 cents) per hour for those who work as part-timers, the newspaper said, citing its own undercover investigation.

It also accused the restaurants of demanding part-time employees work full-time without corresponding benefits.

Li said local trade unions in other provinces, such as Hubei, Fujian and Liaoning, had responded quickly by starting investigations into similar unlawful practices.

He said the federation and the Ministry of Labor and Social Security will jointly launch a nationwide check next month on payment, minimum wages and labor contracts in enterprises.

Li said the federation will encourage foreign companies' to set up trade unions so that a satisfactory wage system could be formulated.

"We are sure that McDonald's, KFC - as world-famous brands - will set a good example," Li said. "At the same time, we believe the event won't delay their process of establishing trade unions."