As part of its ongoing effort to find and destroy any melamine-tainted milk remaining on the market, the Chinese government is recalling 170 tons of milk powder laced with the industrial chemical.

Officials announced the recall after finding that more cases of the tainted milk–which was supposed to be destroyed or buried in 2008–had been repackaged and placed back into the marketplace.

In addition to the recall, authorities closed two dairy companies in the northern region of Ningzia, seized 72 tons of the implicated milk powder, and are actively searching for the rest, according to the China Daily news.

The discovery comes in the context of a country-wide crackdown on food safety. After the 2008 melamine milk scandal killed six infants, sickened over 300,000, and drew international criticism, Chinese authorities are ramping up the enforcement of newly enacted food safety laws.

In recent weeks, officials have shut down dairies, arrested executives involved in selling tainted products, and in November the government executed two businessmen for their involvement in the 2008 melamine scandal.

The ongoing effort to remove tainted milk from the marketplace is set to end Wednesday. It remains unclear whether recent findings will cause authorities to extend the campaign.

Melamine is an attractive adulterant because it boosts nitrogen content, making dairy products show artificially high protein levels in quality assurance tests.