By Heather Chen, CNN

(CNN) — A Muslim cleric has been arrested on charges of blasphemy and hate speech in Indonesia after his decision to allow women to preach and pray beside men sparked a backlash in the world’s largest Muslim-majority nation.

Panji Gumilang, 77, who runs the Al-Zaytun boarding school in the district of Indramayu in West Java, was arrested on Tuesday, Indonesian National Police official Djuhandhani Rahardjo told reporters outside its Criminal Investigation Agency in Jakarta.

In the past, the school, home to roughly 5,000 students, has faced public backlash over its unorthodox practices like allowing men and women to pray alongside each other and women to become imams. Unlike other Islamic boarding schools in Indonesia, its prayer sessions do not follow gender segregation, angering some religious groups.

“Investigators took legal action,” Djuhandhani said on Tuesday. “(Panjiwill be) detained in the Criminal Investigation Agency’s detention facility for 20 days,” he added.

Police did not specify what Panji had said or done that constituted blasphemy but said they were acting on public complaints.

In June, Indonesia’s Islamic Clerical Council said it was investigating Al-Zaytun for “misguided religious practices,” according to CNN affiliate CNN Indonesia. If found guilty of blasphemy and hate speech, Panji faces a maximum 10 years in prison.

Panji’slawyer Hendra Effendy called for calm from his supporters.

“He is after all, a public figure with millions of supporters… With all this happening, we don’t know what could happen,” he told CNN Indonesia.

One of Panji’s supporters, who did not wish to be named for fear of reprisals, told CNN his arrest was “unjust” and reflective of the country’s turn towards the religious right.

“So he went against (the curve) – does he deserve to be punished for his compassion,” the supporter asked.

Rise in blasphemy cases

Most mainstream schools of Islam around the world segregate men and women during prayers and do not permit women to lead mixed gendered prayers or deliver sermons.

Indonesia is the world’s largest Muslim-majority nation, with 231 million Muslims.

Although it has an overwhelming Muslim majority, it is constitutionally secular and officially recognizes six religions – Islam, Protestantism, Catholicism, Hinduism, Buddhism and Confucianism.

Historically the country has practiced a tolerant and pluralist form of Islam. However, it has seen a rise in religious conservatism in recent years.

Strict Islamic laws are also enforced in some parts of the country, including the semi-autonomous Aceh province, where alcohol and gambling are banned and public floggings take place for a range of offenses including homosexuality and adultery.

Panji was “supportive” of Muslim women becoming imams and leading others in prayer, something which “isn’t normal in Indonesian society,” said Andreas Harsono, Indonesia researcher at Human Rights Watch.

“He has been promoting gender equality within Islam and this has angered the conservatives. There is nothing wrong with him (a Muslim cleric) promoting women’s rights – something is terribly wrong with blasphemy laws,” he added.

Rights groups say that religious freedom and tolerance are “under threat” in Indonesia and blasphemy laws were being “increasingly weaponized” against religious minorities and people deemed to have criticized Islam.

One of the highest profile blasphemy cases was that of Basuki Tjahaja Purnama, an ethnic Chinese Indonesian widely known as Ahok and Jakarta’s first non-Muslim governor in 50 years.

He went on trial for blasphemy in 2017 after angering hard-line Muslims by referencing a verse from the Quran while campaigning for re-election in 2016.

Despite making a public apology, he was jailed for two years – a verdict met with scrutiny and condemnation by many Indonesians and observers in the international community. The case was widely seen as a test of religious tolerance and free speech in Indonesia.

“Blasphemy cases have been increasing drastically over the years,” Andreas of Human Rights Watch said. “Officials in Indonesia are using these laws more frequently against religious minorities in the name of ‘religious harmony’ and it’s (grown) more and more toxic.”

“It is becoming an increasingly Islamized state and there will be many more consequences… for people whose views are considered to be against the Islamic establishment,” he said, referencing controversial amendments to its criminal code set to be passed by 2025.