Catholic leaders from around the world have expressed their support for Australian Sister Patricia Fox, who was recently detained and is now facing deportation for taking part in protest rallies.

Fox, a missionary of the Sisters of Notre Dame de Sion (NDS), was detained by immigration officials last week for allegedly violating a law barring foreigners from taking part in protest rallies.

The 71-year-old nun, who has been advocating for the rights of farmers and indigenous people in the Philippines for 27 years, was later released but still faces an investigation and possible deportation over her alleged political activities.

The Ecumenical Bishops' Forum denounced the government's treatment of Fox in a statement released on April 19.

"We express outrage at this evil-doing," the bishops said, as reported by UCA News. "We cannot comprehend why church people become targets of political persecution. When has it become a crime to accompany the poor and the oppressed in their struggle? When has it become a crime to preach the words of God and live-out the works of Christ?" they added.

The Sisters of Our Lady of Sion in Australia also condemned the nun's arrest and called on Christians to "stand their ground" in showing their solidarity with the poor.

Fox's colleague in Rome has called on the Philippine government to abandon its plans to deport her.

"We ask the government of the Philippines to allow Sister Pat and other fellow church people to continue their missionary work in the Philippines," said NDS Superior General Sister Mary Babic, as reported by Business Mirror.

"We believe that Sister Pat and other religious and church people like her are a blessing and are blessed be able to work with and be among the Filipino people," she added.

Last week, presidential spokesman Harry Roque released photos as evidence that the nun had spoken at a rally in Davao City on April 9.

The spokesman said that the photo was released to dispute the statement by the Catholic Bishops' Conference of the Philippines (CBCP) that the nun has never spoken at the rallies, PhilStar reported.

President Rodrigo Duterte said he personally ordered an investigation into Fox because of her "disorderly conduct." He contended that the nun should be prohibited from entering the Philippines on the grounds that her criticisms of his administration constitute a "violation of sovereignty."

He said that Fox should instead direct her criticisms to the Australian government over the way it handles refugees trying to enter the country.