According to Yelp’s content guidelines, “the best reviews are passionate and personal.” Yet one Texas couple found out the hard way that a passionate review can result in an aggressive lawsuit and potential financial devastation.

When Robert and Michelle Duchouquette hired a Dallas petsitting company, Prestigious Pets, to watch their two dogs and fish in October of last year, they said they had a sub-par experience. According to the one-star review Michelle Duchouquette left on the company's Yelp page, “We have a camera on the [fish] bowl and we watched the water go from clear to cloudy. There was a layer of food on the bottom from way too much being put in it.”

Michelle also complained about the fees Prestigious Pets charged. “I left a note asking for our keys to be left when the walker left the last day,” she wrote. “They charge $15 to get them back at a later date. The walker did not leave the keys and they are going to charge me to get them back.”

As a result of Michelle’s single review, which is still visible on Yelp, Prestigious Pets hit the Duchouquettes with a massive lawsuit alleging defamation and violation of a non-disparagement clause that could cost them up to $1 million. The Duchouquettes say the clause was buried in the contract.

Here’s what it states:

“In an effort to ensure fair and honest public feedback and to prevent the publishing of false or libelous content in any form, your acceptance of this agreement prohibits you from taking any action that negatively impacts Prestigious Pets LLC, its reputation, products, services, management, employees or independent contractors."

Paul Alan Levy, an attorney for the consumer watchdog organization Public Citizen who is now is representing the couple, told AlterNet that the company’s complaint seeks “actual damages, punitive damages and damages for the infliction of emotional distress.”

The Duchouquettes are not backing down, arguing in a district court on Thursday that "Prestigious Pets cannot prove the review was false, defamatory or made with malice; that it caused damage to the company; or that the non-disparagement clause waived the Duchouquettes’ right to free speech,” according to a statement from Public Citizen.

While the case may seem absurd, Levy emphasized that its implications are quite serious, as hidden disparagement clauses threaten to muzzle criticism or simply intimidate people from speaking openly about their consumer experiences. "The threat of litigation discourages people from expressing their views,” he said, noting that he sees far more non-disparagement clauses today than he did 10 years ago.

Such measures are potentially far-reaching in an era when many turn to online media to share tips, report corporate wrongdoing and weigh consumer choices. Meanwhile, Yelp itself faces accusations that it is not a neutral medium; the company has been deluged with accusations that it is tinkering with its review system in order to pressure businesses into paying more for advertising.

As for Yelp’s response to the Prestigious Pets affair, readers who visit the company’s page will see the following popup message: “This business may be trying to abuse the legal system in an effort to stifle free speech, including issuing questionable legal threats against reviewers. As a reminder, reviewers who share their experiences have a First Amendment right to express their opinions on Yelp.”