Filipino Senator Leila De Lima called on the cabinet on Tuesday to declare President Rodrigo Duterte unfit to lead and labelled him a "serial killer" who should be forced out of office.
"There is no more doubt that our president is a murderer and sociopathic serial killer," De Lima told reporters.
She called on ordinary Filipinos to stand up and voice their opposition against Duterte's rule.
De Lima said the constitution allows for a majority in Duterte's cabinet to force him to step down by ruling that he was mentally incapacitated, and urged it to do so.
The remarks from one of Duterte’s chief critics came after she was charged with allegedly receiving money from drug dealers inside the country's prisons.
The charges stemmed from allegations first made by Duterte, but she insists the charges are manufactured to silence her, as well as intimidate other people who may want to speak out against the president.
She could be detained anytime, although the courts hearing the cases must issue an arrest warrant.
When asked about De Lima's comments, presidential spokesman Ernesto Abella simply described them as "colourful language" and pointed out that Duterte would allow public demonstrations against him.
Duterte, 71, won the presidential election last year after promising during the campaign to eradicate drugs in society by killing thousands of people.
More than 7,700 people have been killed in the narcotics crackdown since Duterte took office on June 30, about 2,500 during police operations, while thousands more are being investigated.
Amnesty International has warned police actions in the drug war may amount to crimes against humanity.
Thousands of Roman Catholics marched in the Philippines capital Manila on Saturday in the biggest gathering denouncing extra-judicial killings and a government plan to reimpose the death penalty for criminals.
Duterte remains popular with many Filipinos, who see him as the strongman needed to fight drugs and corruption, and there is little expectation of a popular uprising against him in the near future.