BEIJING - China's State Food and Drug Administration, or SFDA, on Sunday began to check for food companies processing lime-preserved eggs with copper sulphate, following a scandal highlighted in a media report.

On Friday, China Central Television reported that some egg processing plants are suspected of using copper sulphate in the pickling of lime-preserved eggs, a black-colored cold dish popular around the country.

Copper Sulphate can be poisonous if swallowed.

The SFDA ordered the Jiangxi provincial food and drug administration to investigate the issue immediately, and required industrial and commercial administrative departments, quality supervision departments as well as food and drug administrative departments nationwide to supervise and examine all producers of lime-preserved eggs.

Food additives and processing aid will be the focus of the supervision, said the SFDA, adding that companies found using copper sulphate to process preserved eggs will have their production licenses suspended and be punished strictly according to law.

People suspected of violating the criminal law will be transferred to the police, said the SFDA.