Retirement planning and mutual fund giant Principal Financial said on Tuesday that more staff has improperly traded then originally believed.

Although it wouldn’t specify the number, Principal said in its latest Securities and Exchange Commission filing, that employees, including two portfolio managers, timed the market in their own accounts a few years ago.

One former employee has already settled with the company for his market timing in a 401(k) plan, and the company said it was "aggressively reviewing" other fund managers to see if they did the same.

Since 2000, Principal said, no portfolio manager has timed the market. But between 1998 and 2000, it admitted that $180,000 was made by employees due to rapid in-and-out trades. Most of those employees have since left.

"We do not permit or condone any behavior that is in any way inconsistent with that responsibility," Principal Chairman J. Barry Griswell said.

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