A U.S. automotive safety agency adjusted its guidelines on how manufacturers may reference safety ratings.

The National Highway Traffic Safety Administration (NHTSA) announced Wednesday that companies may no longer tout safety ratings with decimal points or ratings above five stars. The policy change comes three months after electric car manufacturer Tesla Motors bragged of an all-time high 5.4-star safety rating for its Model S sedan.

"Our 5-Star Safety Ratings Program serves as one of the most trusted and reliable resources to help the driving public select vehicles based on unbiased safety ratings," NHTSA Administrator David Strickland said in a statement.

In its announcement of the new guidelines, the NHTSA wrote that any auto companies that break the updated guidelines going forward will be "misleading the public."

"Of all vehicles tested, including every major make and model approved for sale in the United States, the Model S set a new record for the lowest likelihood of injury to occupants," reads an Aug. 19 Tesla Motors press release on the 5.4-star rating.

A Tesla spokesperson declined to comment on the updated NHTSA guidelines.

The NHTSA adjustment comes just one day after the agency announced it's launching an investigation into a recent string of Tesla car fires. Media reports documented three Model S fires during a five-week period leading up to Nov. 6.

In fact, Tesla founder Elon Musk asked the NHTSA to conduct the investigation because of what he considered to be overblown coverage of the car fires, or as he put it, "seeking to make a sensation out of something that a simple Google search would reveal to be false."

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