Representatives for Harman were unavailable for comment Monday. Analysts have suggested that smartphones and tablets could take over the so-called auto infotainment function in vehicles, displacing the navigation-system makers.
Shares of Garmin slumped 8.6% to $38.20 Monday and hit a low of $37.82 for 2012. The stock already was under pressure Monday after Oppenheimer raised concerns about the lingering effects from the economic weakness in Europe, but the selloff accelerated during Apple's annual Worldwide Developers Conference in San Francisco.
Garmin's automotive and mobile division is the company's largest revenue contributor.
Over the past year, Garmin shares and sales have risen as stronger performances in Garmin's other businesses--outdoor, fitness and marine, and aviation--have offset declines in its portable navigation device segment.