Philippine President Rodrigo Duterte is facing opposition from one of the country's most powerful institutions and one that the country's leaders have often been loath to take on - the Roman Catholic Church.

Priests and bishops the Southeast Asian nations that is overwhelmingly Catholic were seen as being initially quiet after Duterte assumed office in the middle of 2016 and began a violent crackdown on suspected drug dealers, New Europe reports.

In just nine months Duterte's contentious war on drugs has led to the death of more than 8,000 dead people.

New Europe cited a report in USA Today online, that the powerful Catholic Bishops' Conference of the Philippines issued a recent pastoral letter that condemned Duterte's war on drugs as a "reign of terror."

On March 19 the Catholic bishops issued a pastoral letter against the death penalty saying, "Even with the best of intentions, capital punishment has never been proven effective as a deterrent to crime.

"Obviously it is easier to eliminate criminals than to get rid of the root causes of criminality in society. Capital punishment and a flawed legal system are always a lethal mix," said the bishops without naming Duterte in their powerfully worded letter.

"And since in any human society there is never a guarantee of a flawless legal system, there is always the great likelihood that those without capital will get the punishment more quickly because it is they who cannot afford a good lawyer and a guarantee of due process."

They noted that as a law the death penalty directly goes against the principle of inalienability of the basic human right to life, enshrined in most constitutions of countries that signed the universal declaration of human rights.

They called for the Catholic faithful to pray fervently for the legislators of the Philippines as they were they preparing vote on death penalty in the country's Senate.

"As a church we don't want killings," Fr. Jerome Secillano, executive secretary of the conference, which issues guidelines and policy for the Catholic Church told USA Today.

"But it's becoming the new normal in our society. There's killing everywhere. The church right now is speaking forcefully against these issues."

Duterte has issues a number of strongly worded criticisms of the Catholic Church, often using provocative language such as calling Pope Francis "a son of a bitch," and last month called the church one of the "oligarchs of this country."

Despite the Church's condemnations, his war on drugs did not slow down as the Philippines celebrated Easter: when there were 39 reported drug-related killings.

The USA Today reported noted that the Catholic Church is not the only institution taking on Duterte.

A formal impeachment complaint was filed I March against him by Rep. Gary Alejano for crimes committed during the war on drugs and corruption allegations that claim Duterte has amassed $40m in unexplained wealth.

IMPEACHMENT COMPLAINT AGAINST DUTUERTE

The opposition lawmaker the impeachment complaint against Duterte, accusing him of crimes ranging from abuse of power to running his own "death squad" when he was mayor of Davao.

But the president dismissed the claims, as he looks to ramp up his deadly war on drugs and seeks to silence any dissident voices, Vice News reported.

In making his complaint Alejano admitted it would be an "uphill battle" to impeach the president given support for him in both houses of parliament but said it would give the people of the Philippines a chance to voice their opinion on Duterte.

"We wanted to give him the chance to run the country," Alejano said. "But what we're seeing so far is a clear indication of his policies, of killing without trial and due process of law. That is very dangerous to our democracy."

On April 24, a Filipino lawyer filed a complaint at the International Criminal Court in The Hague accusing Duterte and 11 other Philippine officials of mass murder and crimes against humanity.