Drilon issued the subpoena upon request of Sen. John Osmeña, chairman of the Senate committee on government corporations and public enterprises that is investigating the rehabilitation.
The issuance of the subpoena came following a statement of the Sandiganbayan that it would respect a subpoena for the appearance of Estrada. The Sandiganbayan has physical custody of Estrada, who is standing trial before the anti-graft court for plunder.
Osmeña set the Estradas testimony on Dec. 17 at 9 a.m. at the Recto-Laurel rooms of the Senate.
He said that Estrada would be asked to testify on his claims that Manila Rep. Mark Jimenez, reportedly acting in behalf of Impsa, allegedly offered $14 million for the approval of a government contract with Impsa for the rehabilitation of the CBK plants. Estrada had stressed that the offer did not come directly from Impsa.
Impsa had denied ever bribing any government official to bag the CBK contract.
Estrada had said he rejected the Impsa contract on advice of then Finance Secretary Jose Pardo and former Justice Secretary Artemio Toquero because the contract included sovereign guarantee.
"We also invited Pardo and Toquero to testify in the Dec. 17 hearing," Osmeña said.
The committee investigation is an offshoot of a privilege speech of Sen. Sergio Osmeña III charging that the rehabilitation of the CBK power plants was "needless" as claimed by some engineers of the National Power Corp. (Napocor).