Iconic Charlie the Tuna of advertising fame never seems to learn what the StarKist Co. wants, but Thursday it was the company's turn to learn a costly lesson in what federal antitrust prosecutors want.

The last of three companies involved, StarKist agreed to plead guilty to a felony charge of price fixing on canned tuna fish. It faces a whopping $100 million maximum fine, one to five years of probation and an unidentified amount of restitution, according to documents filed with the U.S. District Court for the Northern District of California.

Pittsburgh-based StarKist, a unit of Dongwon Industries, issued a statement saying it had cooperated with the U.S. Department of Justice during the course of its investigation and has accepted responsibility for its conduct.

Company president and CEO Andrew Choe said, “We will continue to conduct our business with the utmost transparency and integrity. While this process is long-term in nature, we have addressed the necessary actions required in this plea agreement, including continuing to strengthen related compliance best practices.”

Terms of the plea deal were not made public, and a sentencing hearing has not yet been scheduled.

Meanwhile, there are some key takeaways for general counsel in the prosecution:

“The dollar value is pretty high,” noted Colin Kass, a partner in the Washington, D.C., office of Proskauer Rose and co-chair of the antitrust group. “It shows that the U.S. Department of Justice is continuing to aggressively pursue criminal antitrust cases.”

The StarKist case was part of an industry probe by the Justice Department involving the three largest U.S. sellers of packaged seafood—StarKist, Bumble Bee Foods and Thai Union Group and its U.S. subsidiary, Tri-Union Seafoods, which sells Chicken of the Sea tuna.

Thai Union revealed in 2015 that it had entered DOJ's leniency program and was granted immunity from prosecution in return for disclosing how the collusion worked and who was involved.

Bumble Bee pleaded guilty to one count of price fixing in May 2017, and agreed to pay a $25 million fine that could escalate to $81.5 million in the event that the company is sold to another.

Bumble Bee's CEO was indicted for participating in the conspiracy in May of this year. Three other Bumble Bee executives have already pleaded guilty.

The price-fixing investigation began shortly after Thai Union sought to merge with Bumble Bee in 2014. The price collusion may have come to light during the attempted merger, Kass explained, because “companies produce thousands of pages of documents relating to competition.”

One of the things investigators found was that, while the demand for tuna was dropping over the years and the supply remained plentiful, the three companies were not lowering their prices. Prosecutors also found emails, texts and evidence of communication among the companies.

Kass said the prosecution “reinforces the concept that companies need to be very careful about inter-firm communications.”

The consequences can be very costly, Kass pointed out, not only for an antitrust case that can carry treble damages but also for the civil lawsuits that inevitably follow.

That's what happened here. Several grocery wholesalers and retailers, including Walmart Inc., sued the three companies for millions of dollars in overpayments for the tuna.

Kass advised, “If you are planning to merge, and especially if it is a concentrated industry, it is important to do some level of due diligence on emails and text messages before you file for approval of the merger.”

Otherwise, it could be DOJ saying, “Sorry, Charlie.”