Subaru Corp. spokeswoman Miyuki Yasuda said the company was checking and a report to the government would be coming as soon as possible.
Japanese media reports said unauthorized people had inspected vehicles at two Subaru plants in Gunma prefecture, northwest of Tokyo.
The government ordered automakers to check their inspection procedures after Nissan Motor Co. apologized for allowing unauthorized employees to do final vehicle checks for years.
Subaru, formerly called Fuji Heavy Industries, is partnered with Toyota Motor Corp., a top shareholder. Toyota and Honda Motor Co. had said they did not have dubious inspections. Toyota said it was checking with Subaru on the reported irregularities.
The transportation ministry said it had not gotten a report from Subaru.
Nissan is recalling more than a million vehicles in Japan to re-inspect them, and has set up an investigative team that includes a third party to get to the bottom of the scandal and prevent a recurrence.
The wrongdoing, spanning its six plants nationwide over many years, has stunned the public and cast a shadow over this nation’s prized “monozukuri,” or production, reputed for quality, order and meticulousness.
The problem does not affect Nissan vehicles sold outside Japan and is not believed to have affected vehicle safety as they were final-stage checks.
But the scandal raises serious questions about ethics and professionalism at Nissan, which makes the Leaf electric car and Infiniti luxury models, and is allied with Renault SA of France and Mitsubishi Motors Corp. of Japan.
The auto industry has been hit by a series of scandals.
Nissan took a controlling stake in Mitsubishi Motors last year after that company was caught inflating fuel economy figures for its minicar models, which are also sold under the Nissan brand.
Japanese supplier Kobe Steel acknowledged recently it had systematically falsified data on its products, including steel, aluminum, copper and other materials, affecting some 500 companies including major global automakers, as well as the aircraft, electronics and railway industries.
Volkswagen AG of Germany acknowledged in 2015 that it had equipped its diesel cars with illegal software that enabled cheating on U.S. emissions tests. Volkswagen has agreed to more than $20 billion in fines and civil settlements over the scandal.
Air-bag maker Takata Corp. filed for bankruptcy protection after some 100 million air-bag inflators were recalled worldwide. The defect has been linked to 19 deaths and dozens of injuries.
AP Business Writer Yuri Kageyama can be reached at https://twitter.com/yurikageyama