Constellation Energy CEO Mayo Shattuck has agreed to testify in person at regulatory hearings on Exelon Corp.'s proposal to buy Constellation and BGE, according to new filings with the Public Service Commission. The move comes after the Maryland Energy Administration asked the PSC to subpoena him as a witness, arguing that he needed to be available to answer many questions about the merger and his planned role at the combined company.

"In an effort to be fully transparent and to resolve any possible confusion, the Applicants will voluntarily produce Mr. Shattuck as a live witness in the proceedings on a panel with Mr. [Christopher] Crane," the No. 2 executive at Exelon, the companies' lawyer J. Joseph "Max" Curran III, wrote in a filing made Thursday.

That wasn't good enough for EDF Group, the French-controlled electricity giant that is Constellation's partner in a large nuclear energy venture. EDF has expressed concern that its multibillion-dollar investment in Constellation would be at risk if Constellation is absorbed by Exelon.

"... EDF submits that Mr. Shattuck does not need the protection of mr. Crane to address the many outstanding questions related to the proposed merger..." EDF's Thursday filing said.

Look for lawyers to grill Shattuck about his responsibilities, why he thinks the deal is a good one and how he would simultaneously act as chairman of the board and an employee reporting to Crane.