Wolfson said the agency has only taken such a step three times previously in 11 years.
"It is very rare in our history to file this sort of suit," Wolfson said. "That should indicate to the families how seriously the CPSC staff is taking this situation."
The complaint, filed within the agency and to be handled by an administrative law judge, took Baby Matters' founder, Leslie Gudel, by surprise. Having been in talks with the CPSC for months over some corrective-action plan, she had expected a notice asking parents to stop using the chair.
In anticipation of that, Gudel, who is also a Phillies reporter and anchor for Comcast SportsNet, shut down the company on Nov. 12. Baby Matters had 13 employees, had sold more than 160,000 Nap Nannys and was on track to exceed $6 million in revenues this year - a 65 percent increase over last year, Gudel said.
She issued a statement Wednesday defending the safety of the Nap Nanny, which she began marketing nearly four years ago to help parents with infants who were difficult sleepers. One of her two children fit that category and was the inspiration for the chair, Gudel had said in an interview in April.
"Nap Nanny has helped thousands of babies and their tired parents the last four years and when used properly, no infant has ever suffered an injury requiring medical attention," Gudel said.
In four of the five deaths, none of which occurred in the Philadelphia area, the Nap Nanny was placed in a crib. Warning labels sewn on the chair state its use is intended for the floor only, and that the three-point harness should be secured around the infant.
The CPSC's actions Wednesday, coming after months of talks between the CPSC, Gudel and her lawyers, follow a July 2010 recall the agency and Gudel agreed to involving two earlier versions of Nap Nanny.
The CPSC sought that measure after learning of an infant death involving Nap Nanny and hearing of babies managing to get themselves sideways while in the angled, high-density-foam chair. As part of that recall, improved warnings and instructions were issued for the Gen2 model, and customers were asked to discontinue using Gen1.
Earlier this year, the CPSC became aware of three other deaths, all with some alleged connection to the first or second generation of Nap Nanny. That led to protracted discussion with Gudel and her lawyers on a plan to remind consumers how to properly use the Nap Nanny.
While those talks were ongoing, a fifth death occurred in July - involving the latest version of the product, Nap Nanny Chill, launched in January 2011 with slightly higher sides and a more snug contour. That prompted the CPSC to file the complaint, alleging safety concerns with the Chill.
Wolfson said his agency also has more than 70 incident reports of children nearly falling out of the Nap Nanny.
He said the CPSC has informed retailers of its actions but would not say whether they are prohibited from continuing to sell the Nap Nanny.
Contact Diane Mastrull at 215-854-2466 or firstname.lastname@example.org, or @mastrud on Twitter.