Virtu Financial Inc. expects to be sued by the Securities and Exchange Commission after talks failed to settle a dispute over the firm’s safeguards for trading data. The shares fell in extended trading.

The New York-based wholesale brokerage said in a filing Friday that the agency had zeroed in on its “information barriers policies and procedures” and sent a Wells Notice indicating a lawsuit was likely. While Virtu said it had cooperated with the inquiry, it wasn’t able to reach a settlement and “intends to defend itself vigorously.”

In a statement, Virtu said that “there is no evidence that anyone actually improperly accessed or used any client information and our policies strictly forbid employees from doing so.” The firm added that it had voluntarily told the regulator about the issue three years ago, and that officials hadn’t found evidence that data was improperly accessed.

A representative for the SEC declined to comment. The stock dropped more than 4% after the disclosure and was down 3.4% as of 5:45 p.m. in New York.

The agency’s probe is focused on who at Virtu could access post-trade data from January 2018 to April 2019, Bloomberg has reported. Firms like Virtu that both make trades on behalf of clients and make markets themselves segregate parts of each activity’s information. Regulators can be concerned where there is a chance one side got to see each others’ information, beyond what is allowed.

Separately, Virtu is fighting the SEC’s plans for a sweeping market structure reform. Chief Executive Officer Doug Cifu has sharply criticized SEC Chair Gary Gensler over the plan, which would upend how stock trades are made and could disrupt parts of the firm’s business model.

(Updates with share price move.)