In June, the Transportation Department delayed long-awaited rules mandating back-up cameras for as much as another 18 months — a blow to safety advocates who have sought cameras to improve rear visibility. It was the fifth time the rules have been delayed, and is a victory for automakers that have fought the mandate, saying it is too expensive.

The suit Wednesday was filed by Consumers Union — the parent of Consumer Reports, Advocates for Highway and Auto Safety, Kids And Cars, Inc., and two parents: Dr. Greg Gulbransen and Susan Auriemma. Auriemma of Manhasset, N.Y. backed over her 3-year-old daughter Kate in her driveway in 2005, injuring her; Gulbransen of Syosset, N.Y., backed over his 2-year-old son Cameron in his driveway in 2002, killing him.