Workers at the recently sold Jinro Co. are in opposition to the consortium that has bought the distiller. Union bosses at six provincial soju makers and Oriental Brewery Co., based in South Korea's capital, Seoul, have complained to the anti-trust watchdog, the Fair Trade Commission.

Unions believe that the acquisition of Jinro by a group led by Hite Brewery, South Korea's largest brewer, is a clear violation of the anti-monopoly law.

"The acquisition also will threaten the right to survival of many workers through unfair competition," union leaders said.

Speaking to Asia Pulse, a labour union chief, on condition of anonymity, said: "The management of other soju makers are acting behind the scenes to block the acquisition as they refrain from explicitly publishing their sales data due to sensitive issues like taxes."

Earlier this month, the Hite-led consortium signed a formal agreement to acquire Jinro for KRW3.41 trillion (US$3.36bn). The distiller has been in court receivership for just over two years.