What the subpoena signals
The SEC staff can issue subpoenas only after the Commission has authorized a formal investigation, so receiving one means the inquiry has moved past informal requests. It does not by itself mean you are accused of anything, because subpoenas go to companies, employees, auditors, and others who simply have relevant information. You can ask the staff about your role and request a copy of the formal order, which describes the general subject of the investigation. Ignoring a subpoena can lead the SEC to seek a court order enforcing it. The SEC is a civil agency, but it shares information with criminal prosecutors, so testimony should be approached with that in mind.
Producing documents carefully
Suspend any routine deletion right away, including on personal phones and messaging apps used for work. Review the subpoena's definitions and time period closely, since the scope can often be clarified or narrowed by discussion with the staff before production. Productions are usually made in a specified electronic format with a log of anything withheld as privileged, and documents once produced cannot easily be taken back. If you work for a company that has also received a subpoena, find out whether its counsel represents you or only the company, since your interests may not line up.
Before you testify
Testimony is taken under oath, recorded by a court reporter, and can be used in later proceedings. You have the right to counsel, and preparation should include a careful review of your own documents. If there is any criminal exposure, the Fifth Amendment privilege may be available, but invoking it in an SEC matter can permit an adverse inference in the civil case, so the decision needs weighing in advance. Once we have read the SEC subpoena and understood your connection to the matter, we decide whether to approach the staff about scope, timing, or your status.