In an uncommon move, Virtu filed a lawsuit against the U.S. Securities and Exchange Commission on Tuesday, claiming that its chief regulator had failed to reply to a request for public documents. Virtu, a market maker with a sizable equity business, claimed it filed a Freedom of Information Act (FOIA) request in June to ascertain whether the SEC had complied with legal requirements to assess potential investor harm and market risks while taking new rules for the handling and execution of retail stock orders into consideration. “What we’re doing is exercising our rights as citizens … to understand what this Chair is looking at and who he’s meeting…