The legal petition listing her name is an unacceptable attack against the mandate holder by the Philippines Government, they added.
"We are shocked that the Special Rapporteur is being targeted because of her work defending the rights of indigenous peoples," said Michel Forst, the Special Rapporteur on the situation of human rights defenders, and Catalina Devandas Aguilar, Chairperson of the Coordination Committee of the Special Procedures.
The UN expert was named in a Government petition filed last month in a Manila court, accused of terrorism and alleged membership of the New People's Army and the Communist Party of the Philippines along with over 600 others.
"The accusation against her comes after the public comments made, jointly with other Special Rapporteurs, in relation to the militarization, attacks and killings of indigenous Lumad peoples by members of the armed forces in Mindanao; this accusation is considered as an act of retaliation for such comments," the experts said.
The Special Rapporteur most recently addressed the issue in a news release on 27 December 2017, which was made in line with the responsibility entrusted to her by the Human Rights Council to report on alleged violations of indigenous people's rights globally. The President's spokesperson reacted with hostility to the news release, publicly accusing the Special Rapporteur of seeking to embarrass the Duterte administration.
"We call on the Philippine authorities to immediately drop these unfounded accusations against Ms. Tauli-Corpuz and to ensure her physical safety and that of others listed," the UN experts said.
"We remind the Philippine Government of its obligations under the Convention on the Privileges and Immunities of the United Nations of 1946, which sets out that United Nations experts have immunity from legal proceedings of every kind of spoken and written acts undertaken in the course of their mandated work," the experts added.
"The attack against the Special Rapporteur is taking place in the context of widespread extrajudicial executions and ongoing attacks against voices who are critical of the current Government, including human rights defenders. The President has himself publicly intimidated Special Rapporteurs.
"Ms. Tauli-Corpuz is a human rights defender," the experts said. "Therefore, the Government of the Philippines has a duty under the Declaration on Human Rights Defenders to guarantee her right to promote and to strive for the realization of human rights."