De Venecia imposed the moratorium last week in the wake of persistent reports about the alleged extortion activities of a group of congressmen known as the "Gang of 5."
Suplico, who is suspected to be a member of the group, invoked the Constitution in opposing the six-month freeze on legislative inquiries.
He quoted Section 21, Article VI of the Charter: "The Senate and the House of Representatives, or any of its respective committees, may conduct inquiries in aid of legislation in accordance with its duly published rules of procedure. The rights of persons appearing in or affected by such inquiries shall be respected."
He said the House leadership cannot just order a suspension on investigations without violating this particular provision of the Constitution.
On Saturday, a day after Mitra voiced his opposition to the moratorium, Rep. Rodolfo Albano (Lakas, Isabela), a staunch De Venecia ally, said only those with "evil designs" would be afraid of a freeze on inquiries.
Under De Venecia’s decision, only investigations of "grave national importance" will be conducted.
He said the moratorium would enable the House to "concentrate on its primary purpose of constructive lawmaking."
Suplico and Representatives Prospero Pichay Jr. of Surigao del Sur, Aniceto Saludo of Southern Leyte, Eduardo Veloso of Leyte and Jacinto Paras of Negros Oriental have been named in various media reports as members of the Gang of 5.
All five have denied that they are engaged in extortion activities. They have named Majority Leader Neptali Gonzales and Deputy Majority Leader Francis Escudero as the source of the reports against them. The two have denied their colleagues’ allegation.
In a resolution, Suplico has asked the House ethics committee to investigate him. He has also offered to discontinue his membership in the opposition Laban ng Demokratikong Pilipino, which chose to keep him as a member.
In a separate resolution, Pichay urged the same committee to investigate Gonzales and Escudero.