BERLIN (Reuters) -Shares in medical equipment maker Gerresheimer plunged as much as 38% on Wednesday after Germany's financial regulator said it was investigating suspected accounting rule violations.

Watchdog BaFin said it would review Gerresheimer's financial statements as of November 30, 2024, adding the company may have recognised revenue for some contracts with customers before the revenue was actually realised.

The shares were down 20% at 0919 GMT, their lowest in 13 years.

Gerresheimer said in a statement that the revenues under review, which were recognised under so-called bill-and-hold agreements in fiscal year 2024, amounted to a "low double-digit million amount".

It said overall revenues in fiscal 2024 were 2.04 billion euros ($2.40 billion) and that it believed that results were "appropriately recognised" in accordance with accounting regulations.

"We take the supervisory authority's investigation very seriously. Transparency, compliance, and corporate governance are very important to us, the company's finance chief Wolf Lehmann said in the statement.

Gerresheimer would cooperate fully with BaFin, it added.

The group, whose products include injector pens for weight-loss drugs, vials and inhalers, said last month that finance chief Bernd Metzner was being replaced by Lehmann, a company outsider with a background in private equity.

It said at the time that Metzner had resigned at his own request.

Metzner has been in the spotlight following the failed sale of Gerresheimer to financial investors and a decline in the company's share price, with activist investor Active Ownership Capital (AOC) recently demanding that his position be re-examined.

AOC, a major shareholder in Gerresheimer, previously said it saw major potential for value creation at the company and called for a strategic review, the second activist investor to do so.

Sensitivities over accounting compliance have increased since the collapse of online payments company Wirecard in 2020 over a 1.9 billion euro hole in its balance sheet, turning the spotlight on regulators who took years to investigate allegations against the firm.

($1 = 0.8498 euros)