The NHTSA said that it launched an inquiry into the timeliness of how Mercedes-Benz alerted owners of about 1.4 million vehicles it recalled in 2017.
Last week, the government agency sent a letter to the automaker's U.S. office asking why the automaker took longer than the required 60 days to alert vehicle owners about recalls.
As part of the inquiry, the NHTSA asked Mercedes to explain how it handled more than two dozen recalls over the last three years. The NHTSA is also investigating how Mercedes handled its part in a massive and growing recall of faulty airbags made by automotive supplier Takata.
In the last few years, the NHTSA has doled out penalties to Fiat Chrysler Automobiles and Honda over delays in reporting issues relating to vehicle defects and recalls to the government in a timely manner.
Mercedes must respond to the letter within three weeks. If the NHTSA finds wrongdoing, the automaker could be subject to civil penalties of as much as $21,000 per day.