Nidec shares slid Monday after the company discovered more suspected cases of improper bookkeeping, heightening fears the world’s biggest maker of mini motors may come under regulatory scrutiny for a potential delisting.

The latest revelations emerged from an external probe that began earlier this month when Nidec found evidence of systemic accounting problems. On Friday, it said in a financial report — submitted after a three-month delay — that it had unearthed new problems. Its car inverter business may have for years underreported duties on second-hand goods exported to China, and a Swiss unit may have exported products without completing the required paperwork.

Nidec’s stock fell as much as 4.8% early on Monday, which was also an ex-dividend date for the company. The shares later recouped much of their losses and were down about 1.8% in late morning trading.