A new U.S. securities regulatory investigation into potential insider trading began in mid-November with the issuance of subpoenas to a number of hedge funds that may have gotten an advance word on corporate takeovers, said people familiar with the matter.

The subpoenas were issued by the Securities and Exchange Commission’s Philadelphia regional office and also went to a number of Wall Street investment houses, the sources said.

The Wall Street Journal, which first reported on the investigation, said regulators are looking into reports of insider trading in at least nine mergers, including Pfizer Inc’s takeover of Wyeth and Merck & Co Inc’s acquisition of Schering-Plough Corp.

The paper reported that regulators have sent out about three dozen subpoenas.

Another deal under scrutiny is the 2007 acquisition of nursing home operator Genesis HealthCare Corp by private equity firms JER Partners and Formation Capital, according to the Journal.

The Genesis HealthCare acquisition already has led to one insider trading enforcement action brought by the SEC’s Philadelphia office, which may explain why regulators there are heading up the investigation.

Read More: – Additional reporting by A. Ananthalakshmi in Bangalore, Reuters