Drilon, who was among the 16 senators who filed a petition questioning the legality of EO 464 last Oct. 11, said the Senate has no choice but to wait for the decision of the Supreme Court on the issue.
Drilon led the 16 senators from both the opposition and pro-administration in questioning the constitutionality of EO 464, which prohibits Cabinet members, along with high-ranking military and police officers, from appearing before congressional hearings without prior clearance from the President.
The senators sought to declare EO 464 unconstitutional for impeding the oversight functions of Congress.
"The critical witnesses all belong to the Executive (branch). At this point, with EO 464 pending before the Supreme Court, we could not proceed with the hearing since they would invoke 464," Drilon said.
Drilon said the controversial executive order affected the Senate inquiry into the North Rail project and other pending high-profile investigations.
Among the Senate investigations effectively halted by the issuance of EO 464 were hearings on the public relations contract with the US-based firm Venable LLP, the alleged electoral fraud committed by the administration in the 2004 election as contained in the "Hello Garci" recordings and the alleged misuse of fertilizer funds by the Department of Agriculture (DA).
The inquiries have mostly focused on the alleged involvement of the President and members of her family in anomalies.
Drilon claimed several irregularities were committed in the North Rail project, citing the study conducted by the University of the Philippines Law Center showing the lack of bidding procedures and questioning the legality of the contract.
Drilon commissioned the UP Law Center to examine the project, which they claimed was "riddled with anomalies."
"The moment 464 is decided upon and assuming that the position of the Senate is sustained by the Supreme Court, then we’ll continue the hearings (on that issue)," Drilon said.
"If not then, we will submit the report on the basis of what was presented before the Senate (by the UP Law Center)," he added.
The $503-million project involves the rehabilitation of a 32-kilometer railway from Caloocan City to Malolos, Bulacan funded by a loan from China EximBank.
North Rail, a government-owned firm, employed the services of China National Machinery and Equipment Corp. for the construction of the railways through an agreement executed between the Philippine government and China on Dec. 30, 2003.
Last week, the Supreme Court tossed to a trial court the petition of rail dwellers and a group of lawyers seeking to void the railway project on the claim that the contract was defective.