Robinhood Markets faces a civil fraud investigation over its early failure to fully disclose its practice of selling clients’ orders to high-speed trading firms, people familiar with the matter said.

The investigation is at an advanced stage and the company could have to pay a fine exceeding $10m if it agrees to settle the Securities and Exchange Commission probe, one of the people said. A deal, however, is unlikely to be announced this month, the people said, and the two sides haven’t formally negotiated a proposed fine, the person said.