MANILA, Philippines — A former justice of the Supreme Court said on Monday that the High Court’s own internal rules barred the initiation of an ouster petition against any of its members after the first year in office.

Retired Justice Vicente Mendoza warned that allowing the ouster petition against Chief Justice Maria Lourdes Sereno to prosper would undermine the constitutional right of magistrates to security of tenure and the independence of the judiciary.

“A quo warranto proceeding filed against a member of the court or any impeachable officer for that matter filed more than a year after assumption of office will undermine the security of tenure guaranteed by the Constitution to public officers who are simply removable by impeachment and ultimately subvert the independence of the judiciary," Mendoza said in an interview on ANC.

Sereno is facing a quo warranto petition , which questions her legal hold on her office, filed by Solicitor General Jose Calida, the government’s top lawyer.

Sereno had indicated that President Rodrigo Duterte may have been behind moves to oust her, following her critical stance on the chief executive’s flagship crackdown on illegal drugs.

Duterte, after denying the allegations, warned Sereno on April 9, "I am now your enemy." He has since hit Sereno in his speeches and has said that she should be removed from office.

Sereno is also fending off attempts to remove her through impeachment in Congress, where she is accused of 27 acts which allegedly constitute enough grounds for her ouster. The House of Representatives, which is dominated by Duterte allies, has yet to vote on sending the articles of impeachment to the Senate, also dominated by the administration, for trial.

Sereno has said she wants to defend herself at the impeachment court, where she believes she will be treated fairly.

Mendoza said that the court’s justices are aware of the prohibition stated under Rule 66, Section 11 of the 1997 Rules of Civil Procedure.

“Nothing contained in this Rule shall be construed to authorize an action against a public officer or employee for his ouster from office unless the same be commenced within one year after the cause of such ouster, or the right of the petitioner to hold such office or position arose,” the rule states.

Sereno was appointed chief magistrate in August 2012, meaning, Mendoza said, the period for filing an ouster petition lapsed in August 2013.

Mendoza said that the current members of the court are aware not only of its rules but also of its previous decisions.

"You cannot bring a suit for quo warrant to test the validity of the title or right of a person who is impeachable by quo warranto—except by impeachment," he said.

The retired justice said that the filing of one’s Statement of Assets, Liabilities and Net Worth is not the sole basis in assessing the integrity of a candidate for a judicial post.

He said that SALNs are just one of the bases for determining the integrity, one of the constitutional requirement for members of the judiciary.

“The SALN is not a requirement of any law or rule of the JBC,” he said during the interview, adding that integrity is not measurable by age, citizenship, length of government service or membership of the bar.

In seeking to question Sereno’s appointment, Calida said that the chief justice failed to meet the constitutional requirement of integrity when she failed to file her SALNs when she taught at the University of the Philippines and submit 10 or more of these documents when she applied for the top judicial post.

Mendoza said, “Filing of SALNs is not enumerated, not required by the JBC.”

The High Court is on a writing break and is expected to resume its sessions on June 5.