The FBI used a mole to secretly record employees at AmTrust Financial Services (AFSI) - Get Report , a whistleblower told the Wall Street Journal Tuesday. AmTrust shares were down nearly 20% in Tuesday afternoon trading. 

Shares were trading at more than seven times their normal volume.

An auditor at the accounting firm BDO USA LLP used a listening device disguised as a Starbucks gift card to secretly record conversations with employees at the insurer. 

The recordings from 2014 were part of a federal investigation being led by the Securities and Exchange Commission into the company's accounting practices. 

Amway has grown into the country's third largest insurer for workman's comp claims over the past 19 years. It had revenue of $5.45 billion in 2016. 

Editor's note: Story has been updated since 11:52 am EST.

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