We may be getting closer to solving the mystery of what’s inside Subway’s ‘100% tuna’ sandwiches thanks to a California judge

The case of Subway’s mystery tuna is turning a new chapter, potentially bringing the world closer to learning the answer to one of the strangest menu controversies in recent memory.

The restaurant chain’s “100% tuna” items have been the subject of intense debate for several years, with various reports and lawsuits making assorted, often conflicting, claims about what is actually in Subway’s tuna sandwiches.

In the latest twist, a federal judge in California ruled last week that a lawsuit accusing the restaurant chain of not actually using tuna fish in its “100% tuna” menu items can proceed, rejecting Subway’s request to throw out the lawsuit.

The lawsuit was brought by two San Francisco residents who initially argued that the packaging used on Subway’s tuna products was misleading consumers. The plaintiffs alleged that these products were actually a “mixture of various concoctions,” although at the time they did not specify what these concoctions were.

The plaintiffs later amended their case in June, when they instead accused Subway of unsustainable fishing practices. In November, the plaintiffs amended their argument for a third time, saying that Subway’s sandwiches and wraps were “bereft” of tuna, and the company had instead been using ingredients including other fish species, chicken, pork and cattle.

Subway has responded to the latest version of the lawsuit by arguing that traces of non-tuna DNA in its products might be the result from eggs mixed in with mayonnaise or unintentional contact with other meat products at restaurants, and moved to have the case thrown out of court, although the judge’s latest ruling means that the lawsuit will continue.

Subway has strongly rebuked the claims as “meritless” since the first lawsuit, even creating a “TunaFacts” page on its website. A Subway spokesperson told Fortune that the company was “disappointed” that the court had declined to have the case thrown out, and that the lawsuit is “reckless and improper,” while reaffirming that the restaurant still serves “100% tuna.”

“We are confident that Subway will prevail when the Court has an opportunity to consider all the evidence,” the spokesperson added.

The lawsuits have kickstarted a wave of independent investigations into what Subway sandwiches are actually made of.

In June 2021, a New York Times reporter sent samples of a Subway tuna sandwich to a food sampling lab in California, which found less-than-encouraging results for Subway. The lab concluded that the sample’s contents were either “so heavily processed that whatever we could pull out, we couldn’t make an identification,” or “we got some and there’s just nothing there that’s tuna.”

But a separate investigation conducted by Inside Edition magazine found different results, with a Florida lab saying that “tuna was definitely in all three samples we received.”

The case of the dubious tuna is not the first time Subway has found itself in hot water over the quality of its products or the truthfulness of its labels.

In 2020, the Irish Supreme Court ruled that the bread used to make Subway sandwiches was not actually real bread, or at least could not legally be called bread because of its high sugar content that exceeded official limits. The court ruled that Subway’s rolls should be classified as “confectionary” instead.

This story was originally featured on Fortune.com