Cloud computing company Heroku may soon face a class action lawsuit after a New York startup uncovered some big performance problems with the online service in which the company helps software coders build and run their software applications.

Earlier this week, class action attorney John Kristensen set up the website Herokuclassaction.com, and he's now running an online advertising campaign, looking for companies that have had performance issues with Heroku. Kristensen, who has tangled with heavyweights like Toyota in the past, says he's ready to bring a false advertising case against the company, which is now owned by online giant Salesforce.com.

"It looks like they have been misleading their customers. It looks like they hid information from their customers," he says. "They were being charged a price for a service that was not provided and the log information prevented people from finding out how well their systems worked."

Heroku is popular in the startup community. It offers what's known as a "platform cloud" or "platform-as-a-service" Basically, this service lets companies set up their websites and other software applications using popular web development tools such as Ruby on Rails and leave much of the heavy lifting to Heroku.

But last month, developers at a startup called Rap Genius discovered that Heroku's heavy lifting wasn't exactly operating the way they expected.

The problem, it turned out, was that Heroku's routers weren't distributing some web requests the way Heroku said they would. Based on Heroku's documentation, Rap Genius thought that Heroku's routers were doing "intelligent routing" – that is, sending new web traffic to servers that were idle. Instead, they assign jobs randomly. So someone visiting the Rap Genius webpage could easily end up on a really busy server. This is not a minor problem. It seriously affects the performance of some Heroku customers, according to Tom Lehman, the founder of Rap Genius, a rap poetry analysis site with close to 15 million unique visitors per month.

To make matters worse, the monitoring tools that Heroku provided didn't log this performance problem. So, while Rap Genius was fielding complaints about their slow website, they had no idea that the underlying bottleneck lay with Heroku, Lehman says. "Our customers got pissed off. We spent a ton of time and money optimizing for the wrong things," he says. "Heroku promised this service. They didn't deliver on it. And if we had known what they were going to provide, we would have drastically changed our behavior."

After Rap Genius blogged about the issue, other Heroku users came forward to report similar problems, and Lehman found discussion of the issue dating back to 2011.

On February 16, Heroku Senior Director of Product Management Jesper Joergensen acknowledged the issues and said the company was going to clean up its product documentation and improve its monitoring tools. The problem affected an older version of Heroku's service, he said, and those who use a new version of the service would not have these issues.

Heroku declined our request for further comment. "Unfortunately, we can't publicly comment on legal matters," said spokeswoman Dana Oshiro in an email. "Heroku is committed to our customers’ success and focused on delivering the best possible product and experience. We'll continue to update our customers via our blog."

Until then, John Kristensen will keep running his ads. He says that the kind of early stage startups that like to use Heroku typically don't want to get tangled up in class action litigation. They worry that it could become a distraction. He's spoken with one customer, who has since backed off. "That being said, I am in the process of drafting a complaint, in case their feet warm up," he told us.

As for Lehman, he wants some of the $20,000 his company pays Heroku each month returned. "We deserve some sort of refund here," he says.

Update – This story has been updated to clarify that some of the Heroku performance problems had been flagged in discussion groups two year earlier.*