Toyota's headquarters in Tokyo have been raided by police, although it is unclear what they were looking for.
A source told Reuters the search was related to last week's arrest of the company's new communications officer Julie Hamp, who allegedly brought a controlled substance into Japan.
The narcotic oxycodone pain killers, which were contained in a parcel Hamp had posted to herself, are illegal in Japan.
Toyota spokesman Ryo Sakai declined to comment due to the ongoing investigation, but added that the company was cooperating with police.
Hamp, who is the company's first female executive, told police she brought the pain killers into the country to relieve pain in her knees. She has been in the role for just two months.
Following the arrest, Toyota President Akio Toyoda expressed support for Hamp and said he believed it was not her intention to violate the law.