“Rights” backed by force are not moral, natural rights, but social rights afforded to a group by a group at the expense of all others outside that group. You say you have the right to know what foods contain GMO but you have no moral Right to punish someone if they do not meet your demands.
In a free market, food manufacturers would not have the option of lobbying a big central government for protection from consumer preference and government would not have authority to prevent any business who wished to label their food as being free of GMO to do so.
If they lied, either way, consumers would lose trust in the business and it’s products. Since the nature of business it to stay in business, paying close attention to consumer satisfaction would be of the utmost importance. After all if they failed, they would be responsible for any damage they caused and there could be no to-big-to fail with out big government.
If people bought more food that was clearly labeled as either containing or not containing GMO, food producers would eagerly undertake the necessary steps to grow their consumer base by creating the types of food consumers demand and provide them the information about the product that proved to generate sales in the marketplace.