DES MOINES, Iowa (AP) — More farmers are filing lawsuits against agrochemicals giant Syngenta in a legal battle tied to the sale of a genetically modified corn seed. Agrisure Viptera is genetically altered to kill corn-eating bugs and is approved by the United States. It was marketed to farmers in 2011.

But China, a major corn market that refuses to buy genetically modified crops it hasn’t tested, had not agreed to import it. It began rejecting U.S. corn last year when Viptera was detected. More than 50 lawsuits have been filed and hundreds more are being prepared. The lawsuits say losing China as a buyer has cost corn farmers more than $1 billion.

Syngenta says the lawsuits are without merit and upholds the right of farmers to use approved new technologies.