The substance, which has also been found in eggs and animal feed, was added to thicken watered-down milk to fool tests that measure protein content.
Chinese authorities suspect that suppliers trying to increase output diluted their milk and added melamine because its nitrogen content can fool tests measuring protein content.
It is used to make plastics and fertilizers, but it is sometimes illegally mixed into food products, including milk, because its high level of nitrogen can help fool tests that measure protein levels.
On Thursday, a government-appointed commission said that Renault's diesel cars failed pollution tests and investigators raided its facilities, raising fears the French carmaker could be caught up in an emissions scandal similar to the one engulfing Volkswagen, which has admitted to using cheating software to fool tests.
But on Monday, the Environmental Protection Agency and California Air Resources Board alleged that other vehicles, including the diesel versions of the 2016 Audi A6 Quattro, A7 Quattro, A8, A8L and Q5 have software that fools emissions tests.
Less than a week earlier, the company admitted that some diesel cars in the United States were equipped with software built to fool emissions tests.
The MPs said Volkswagen, the company which used cheat devices to fool emissions tests on its vehicles, should pay out to people who bought the cars: "Where proven to have misled customers, the company should pay appropriate compensation".
Contaminated products extend beyond drugs, as was made tragically clear this fall when four Chinese babies died and 53,000 were sickened by melamine, a toxic chemical illegally added to watered-down baby formula to artificially increase the protein count and fool quality tests.
One of China's largest milk companies, Sanlu, based in the city of Shijiazhuang, was the most prominent dairy producer found to sell milk products tainted with melamine, a toxic chemical illegally added to watered-down milk to artificially increase the protein count and fool safety tests.
VW admitted equipping some vehicles with software that turned on emissions-control equipment to fool emissions tests, but allowed illegal levels of emissions in normal operation.
