Protesters marched through downtown Bologna demanding the implementation of a law approved by parliament last year that would force Italian companies to specify on labels the origin of the ingredients of foods and drugs.
The Coldiretti agriculture lobby, which organized the demonstration, said more 150,000 people participated.
Coldiretti said large-scale food-processing companies increasingly purchase raw foods abroad at low prices and mix them with Italian-grown products. The result is that it is becoming impossible to identify the origin of the contents of products such as fruits and vegetables, it said.
Such mixing has become a greater concern in light of recent scandals involving tainted products from China, a growing list that includes frozen fish to juice.
Farmer Claudio Pigini said his efforts to grow high-quality tomatoes are not rewarded because he is competing with cheaper foreign imports.
?We are limited in the usage of pesticides by Italian laws in order to avoid making the plant toxic. Having to comply with this rule involves a major expense. On the other hand, one doesn?t know what Chinese farmers use since they don?t do any tests,? Pigini told Associated Press Television News.