(CNN) — The federal government said it will recommend that new cars have rearview video systems -- a move immediately denounced as "insufficient" by safety groups who say the cameras should be mandatory.
The camera and monitor system enables drivers to see whether people or objects are in the blind spot behind vehicles.
The National Highway Traffic Safety Administration (NHTSA) said Tuesday it will add the rearview video systems to its list of recommended features under its New Car Assessment Program, designed to encourage car manufacturers to improve vehicle safety.
But safety groups called the action a stalling tactic, saying the agency is dragging its feet in fulfilling a congressionally imposed deadline to issue a rule on rear visibility.
Passed in 2008, the law had a 2011 deadline. The regulation is now two and a half years overdue.
The NHTSA action "is an inadequate substitute for issuing a mandatory safety regulation," Jackie Gillan, president of Advocates for Highway and Auto Safety, said in a statement. "In fact, safety advocates are concerned that NHTSA's announcement is an attempt to divert attention from their failure to act."
The NHTSA announcement Tuesday came just one day before a group of safety advocates -- including two parents who unintentionally hit their children while backing up -- was expected to file suit against the U.S. Department of Transportation, which includes NHTSA.
The suit is to be filed Wednesday morning by Greg Gulbransen, who reportedly backed over his 2-year-old son, Cameron, in his driveway in 2002, killing him, and by Susan Auriemma, who backed over her 3-year-old daughter, Kate, in her driveway in 2005, injuring her.
Also joining in the suit will be the Consumers Union of the United States, Advocates for Highway and Auto Safety and KidsAndCars.org, those groups said in a statement.
The lawsuit asks the court to direct the DOT to issue a mandatory rule within 90 days.
Rearview camera systems are available on seven in 10 new vehicles, as either standard equipment or an option. But the safety groups say the government's inaction has allowed the death toll in so-called "backover" accidents to grow.
According to the U.S. Department of Transportation, more than 200 people are killed and 17,000 injured every year in backover crashes, when drivers back up over unseen objects behind them.
Children under the age of five account for 44% of the fatalities. In a high percentage of those cases, the motorist is a parent or family member.
In December 2010, NHTSA published a proposed rule and set out to meet a February 2011 deadline for enacting it.
On-board cameras, NHTSA said at the time, could cut in half deaths and injuries due to backing crashes, at a cost of about $159 to $203 per vehicle, or about $1.9 billion to $2.7 billion a year for the nation's 16.6 million fleet of new vehicles. (The price has since fallen, advocates say.)
But the Department of Transportation twice extended the deadline, first to December 2011, and again to February 2012, a deadline it has missed. The DOT said the extension were necessary because of the "large volume of public comments and the complexity of some of the issues."
Transportation Secretary Anthony Foxx said it a statement Tuesday that he remains committed to implementing a new rear visibility rule.
But adding rearview systems to its list of recommended features "will encourage both automakers and consumers to consider more vehicles that offer this important technology."
NHTSA said it would include the video system into its New Car Assessment Program in two phases. Starting immediately, the agency will begin identifying on www.safercar.gov  vehicle models that have the video systems. Next, as soon as the agency is able to verify that systems meet basic criteria, the agency will recognize those vehicles as having this recommended advanced technology feature on the website.