Metro Manila (CNN Philippines, May 16) — Opposition senators have asked the Supreme Court to stop the country's withdrawal from the International Criminal Court (ICC).

In a petition filed before the High Court Wednesday, Senators Kiko Pangilinan, Franklin Drilon, Bam Aquino, Leila De Lima, Risa Hontiveros, and Antonio Trillanes said the executive cannot pull the country out of the international tribunal without the Senate's concurrence.

The "Instrument of Withdrawal" was sent to the United Nations Secretary General on March 15 without the participation of the Senate, contrary to Article 7, Section 21 of the Constitution, the petition said, adding that the provision applies to both entering and withdrawing from a treaty.

It wants the High Court to declare the move as "invalid or ineffective."

"Compel the Executive Department through the Department of Foreign Affairs and Philippine Permanent Mission to the United Nations to notify the United Nations Secretary-General that it is canceling, revoking, or withdrawing (the decision to pull out of the ICC)," the senators urged the Supreme Court.

They added the Supreme Court should stop the executive's move to prevent "dangerous consequences" in the future, as the President and his men "may upend some of the basic norms of our legal system at his or her own behest."

Presidential Spokesperson Harry Roque is confident the petition will be junked.

"Well good luck to them, I don't think there is no legal basis," Roque told reporters in a chance interview.

He said the petition for certiorari and mandamus filed by the senators won't prosper because it requires that the executive committed grave abuse of discretion and made a decision without or in excess of its jurisdiction.

"You cannot allege that on matters of foreign affairs," Roque said. "The courts will always defer to the executive on matters of foreign affairs."

Palace's argument

President Rodrigo Duterte pulled the country out of the international tribunal in March, a month after the ICC announced a preliminary examination on alleged extrajudicial killings in the country. A preliminary examination will determine whether there is cause to go on a full-blown investigation.

Trillanes first told CNN Philippines' The Source in March that he and other senators are filing a petition to question the withdrawal.

Presidential Legal Counsel Salvador Panelo, along with Senate President Koko Pimentel, earlier said withdrawing from the ICC does not need Senate concurrence.

Duterte and his officials also said the withdrawal was not needed in the first place because the Philippines was never a member of the ICC. They argued the country's ratification of the Rome Statute, the treaty the formed the ICC, never took effect as it was nt published on the Official Gazette.

For its part, the ICC said it will push through with its preliminary examination.

Malacañang said it will not cooperate with the probe, and the Philippine Drug Enforcement Agency and the Philippine National Police - the agencies leading the anti-drug campaign - are following its lead.

ICC looks into drug killings

The ICC's review was launched after lawyer Jude Sabio filed a communication against Duterte at the ICC, followed by supplemental information from opposition lawmakers Trillanes and Magdalo party-list Rep. Gary Alejano. They said over a thousand were killed by the so-called Davao Death Squad under the leadership of then Mayor Duterte in Davao City, while thousands more were killed in the war on drugs since Duterte became president.

More than 4,000 suspects were killed in anti-drug operations since the bloody drug war in July 2016, government data show. Local and international human rights groups said Duterte in his public pronouncements ordered or encouraged policemen to kill those involved in the drug trade. They said this resulted in more than 13,000 extrajudicial killings in the drug war.

Malacañang has said there are no state-sponsored killings and it is committed to investigate officers who violate and abuse their authority.

CNN Philippines' Anjo Alimario contributed to this report.