The twin votes in the House of Representatives added to a growing climate of fear that Duterte is determined to silence anyone critical of his war on drugs.
The twin votes in the House of Representatives added to a growing climate of fear that Duterte is determined to silence anyone critical of his war on drugs, which has claimed thousands of lives and led rights groups to warn of a crime against humanity.
Duterte directly drew a link between Tuesday night's vote to cut the Commission on Human Rights' annual budget from 678 million pesos ($1.3 million) to 1,000 pesos and its investigations of the drug war killings and related criticism by its chairman.
"He had it coming," Duterte told reporters late Tuesday, referring to commission chairman Jose Gascon.
"They only gave him 1,000 pesos (about $20) because Congress is angry."
The commission is one of several independent government bodies set up by the constitution to check the power of the executive branch, which controls the country's police and military forces.
The Supreme Court is meant to be another safeguard.
Duterte's allies in the lower house's justice committee on Wednesday also voted to impeach its chief justice after determining corruption allegations against her had substance.
The chief justice, Maria Lourdes Sereno, has been another critic of the drug war.
She wrote Duterte a letter last year expressing concern over him publicly naming seven judges as being involved in the drug trade, warning it made them vulnerable to being killed.
Duterte responded by threatening to declare martial law if Sereno continued to interfere in his drug war.
Should the entire house endorse the justice committee's findings against Sereno, the Senate would convene as an impeachment court.
The Senate still has to review and endorse the vote to slash the rights commission's budget.
The Senate is also dominated by Duterte allies, but it has proved more independent than the lower house and it could still over-rule the moves against the rights commission and Sereno.
Nevertheless, critics warned of authoritarian rule under Duterte -- a self-described socialist who has repeatedly praised late Filipino dictator Ferdinand Marcos and Russian President Vladimir Putin.
"This leads us on a direct path to dictatorship," Senator Francis Pangilinan, leader of the Liberal Party, the country's main opposition group, said in response to Tuesday's vote.
Teodoro Casino, a former House member representing the left wing Bayan Muna party, expressed similar sentiments when commenting on the move against Sereno.
"We see this as part of an attempt to harass and bully the Supreme Court, through Chief Justice Sereno, over her critical stance toward the president," Casino told AFP.
"The institutions designed... to serve as watchdogs to the administration, especially on the issue of human rights, are being attacked and weakened."
Duterte also vowed at the weekend to "destroy" another of his chief drug war critics, Senator Antonio Trillanes.
Another main critic, Senator Leila de Lima, was this year jailed on charges of drug trafficking. Rights groups and European lawmakers describe her a political prisoner.
Duterte easily won elections last year after campaigning on a law-and-order platform, promising to unleash an unprecedented crackdown on illegal drugs in which tens of thousands of people would be killed.
Police have reported killing more than 3,800 people in anti-drug operations since he assumed office 15 months ago.
Many thousands of others have been killed in unexplained circumstances.
Rights groups warn police and state-sponsored gunmen are committing mass murder.
Duterte has said as president he would be "happy to slaughter" three million drug addicts, and repeatedly promised police he would not allow them to go to prison for killing as part of the drug war.
On the campaign trail, Duterte also said he would pardon police officers if they were found guilty of multiple cases of murder for killing in the drug war.
Most Filipinos continue to support the crackdown, according to polls.
But the influential Catholic Church is leading a growing campaign of resistance, which in recent weeks has seen rare street rallies calling for an end to the killings.