Domino's still has nightmares about a prank video posted on the social networking site, YouTube, that got two employees in trouble with the law and tarnished the pizza chain's reputation.

The Ann Arbor-based company became an instant Internet sensation in April 2009 after one franchise employee filmed another sticking cheese inside his nose, sneezing on the food and implying it would be delivered to customers from the store they worked at in Conover, N.C.

Both were fired, and the store closed several months later after sales dropped 50 percent. The two former employees were charged with contaminating food distributed to the public. Michael Setzer, 32, was found guilty and sentenced to 24 months of probation in March. Kristy Hammonds, 31, who was banned last fall from college, is still awaiting trial.

The YouTube episode "certainly was a wake-up call," Domino's spokesman Chris Brandon said. "Now we monitor (social media sites) every day. Someone on my team, it's their full-time job to monitor what's being said."

The episode reflects a growing problem of workers across the country, including in Metro Detroit, who like to gossip about the workplace on social networking sites like Facebook, Twitter and YouTube. This has resulted in employers increasing sanctions against employees.

This year, 21 percent of companies with 1,000 or more workers have disciplined employees for violating social networking policies, compared with 13 percent in 2008, according to a survey by Proofpoint Inc., an e-mail security company in Sunnyvale, Calif. About 9 percent have fired an employee for these violations, more than double from 4 percent two years ago.

"For every case you see in the news, it's really just the tip of the iceberg," said Keith Crosley, director of market development for Proofpoint. "There are many more investigations and breaches that you never hear about."

In at least one case, a worker got into trouble for a photo that seemed to have nothing to do with his job.