Until recently, debates over genetically-modified organism (GMO) labeling have unfolded on a localized, state-by-state level.

But with more than 20 states now considering measures that would make labeling mandatory, and with some major food retailers taking voluntary steps to regulate products containing GMOs, the fight is going nationwide.

From Labeling to Outright Bans

Earlier this month, Whole Foods announced it will label all GMO products in its U.S. and Canadian stores by 2018.

This week, the grocery chain went one step further by proclaiming it would not sell genetically modified seafood. Trader Joe's and a number of other U.S. retailers have agreed to do the same.

With AquaBounty's AquAdvantage salmon slated to become the first genetically modified animal to hit U.S. markets, the retailers' announcements come at a pivotal time.

Federal Fight

In 2012, California narrowly voted down Proposition 37, which would have required labeling on all products with genetically altered material. But some 20 other states -- including Missouri, Iowa, Illinois and Indiana -- have seized the baton and are mulling GMO labeling laws.

Meanwhile, lawmakers like Jared Polis of Denver, Democrat Peter DeFazio of Organ and Democrat Barbara Boxer of California are planning to take the fight to the national level.

Behind The Label

As demands for GMO labeling grow louder, many are wondering what will happen if an individual state does succeed in passing a labeling law.

With an estimated 80 percent of processed foods in the U.S. containing GMOs, labeling would be no small task. What is more, due to the interconnectedness of the country's food system and the economics of production, it's likely that a labeling initiative passed in one state will impact labels in others.

Read More:

• GMO labeling laws on deck in the Midwest (KBIA)
• Whole Foods, others to shun genetically modified seafood (Reuters)
• GMO Poll Finds Huge Majority Say Foods Should Be Labeled (Huffington Post)