Former presidential legal counsel Salvador Panelo on Tuesday warned senator-judges that they could face legal challenges, including a possible petition before the Supreme Court (SC), if they move to lower the constitutional voting threshold required to convict Vice President Sara Duterte in her impeachment trial.

Panelo argued that the Senate impeachment court cannot alter the requirement of a two-thirds vote of all senators without first amending the Constitution, saying any attempt to do so would be an unconstitutional exercise of power.

“Hindi puwedeng baguhin ang 24 as a basis for the two-thirds (vote) nang hindi nilalabag ang Constitution,” Panelo said in an interview.

Under the 1987 Constitution, a public official impeached by the House of Representatives may be convicted and removed from office only with the concurrence of two-thirds of all members of the Senate.

The Senate currently has 20 active members, making the required number for conviction 11 votes.

To recall, the Senate impeachment court’s scheduled proceedings to hear the opinions of four retired justices on whether the 16-vote threshold should remain applicable despite the absence of some senator-judges.

The Senate invited retired Chief Justices Hilario Davide Jr., Artemio Panganiban Jr., and Reynato Puno, as well as retired Associate Justice Adolfo Azcuna, to provide their legal views as amici curiae, or friends of the court.

Panelo, however, maintained that while the Senate may listen to legal opinions, senator-judges cannot vote on a proposal that effectively changes the constitutional standard.

“They can debate, they can discuss, they can analyze until their voices run dry, until their lungs collapse, until kingdom come. But they cannot vote on that issue because it is unconstitutional,” he said.

Panelo said any decision by the Senate to adopt a lower threshold could be challenged before the Supreme Court through a petition for certiorari, alleging grave abuse of discretion amounting to lack or excess of jurisdiction.

He also warned of possible criminal exposure for senators who vote based on what he described as an invalid interpretation of the Constitution.

Citing provisions of the Revised Penal Code on rendering an unjust judgment, Panelo said senators could potentially face complaints if they vote to allow a lower threshold or convict Duterte without meeting the constitutional requirement.

“Those who vote that they can lower the threshold and those who vote to convict based on that lowered threshold could be exposed to criminal prosecution,” he said.