他们的理由是用户有知情权。
现在厂商也有他们的理由，要诉Vermont政府。比如这条新闻里有报道。

" The lawsuit, filed in June, argues that the law is misguided, exceeds the state's authority and confuses consumers by suggesting that GMOs are unsafe with no evidence to support that. The lawsuit alleges the law violates food manufacturers' First Amendment rights by forcing them to label a product in a way they find unnecessary and misleading while also prohibiting them from using the word "natural" on genetically modified foods."

http://www.burlingtonfreepress.com/story/news/politics/2014/08/08/gmo-lawsuit-response/13800873/