The Liberal Party believes the judiciary is being undermined as officials from all branches of government appear to be conspiring to oust Chief Justice Maria Lourdes Sereno.
"What we are seeing is the executive and the legislative branches and some members of the Supreme Court ganging up on Chief Justice Maria Lourdes Sereno through the impeachment process and beyond the bounds of such exercise. Is everyone toeing the line of authoritarianism and the stifling of dissent?" read a statement released by the opposition party on Saturday.
"Regrettably, what we are seeing is the slow weakening of judicial independence and dilution of check-and-balance that endangers democracy and ushers in the rule of autocracy."
The statement was made days after 13 Supreme Court magistrates "forced" Sereno to go on an indefinite leave for "various reasons" that were not elaborated by the high court.
House Speaker Pantaleon Alvarez earlier suggested that the Supreme Court may oust Sereno should it be proven that her appointment as chief justice in 2012 was not valid.
Under the current Constitution, only Congress has the power to remove the president, chief justice, commission heads and other impeachable officials from office.
"Wala sa Constitution 'yun (mag-file sa Supreme Court to question validity) pero accepted practice 'yan sa legal practice. 'Yung validity ng kontrata, ang talagang may jurisdiction du'n ay ang SC (Supreme Court)," Alvarez said.
According to the Liberal Party, "the only constitutional way to remove the Chief Justice is through the impeachment process; the magistrates of the high court should know this no less.
"Any machinations to oust her from office outside of impeachment would be in violation of the Constitution that the justices have been sworn to protect and uphold."
On Friday, Sereno also called on impeachment proponents to give her "her day in the Senate impeachment court."
"That is also what I have been consistently saying to those who asked me to resign. No, I will not [resign]. I will give an account of my actions as chief justice to the people," she said in a forum in Baguio City.
Impeachment proceedings against Sereno started last year after lawyer Lorenzo Gadon filed a complaint that accused the top magistrate of culpable violation of the Constitution, betrayal of public trust, and other high crimes for allegedly failing to declare her full income a decade before she became chief justice in 2012.
Sereno was appointed by former President Benigno Aquino III after former Supreme Court Chief Justice Renato Corona was impeached for undeclared wealth.