A Malaysian Catholic newspaper and church groups cried foul on Friday over a government move to forbid non-Muslims from using the word Allah.
The row could further strain race and religious relations in the country, where many non-Muslims believe their rights are being trampled by the Muslim majority.
The dispute came out in the open after Malaysia's internal security ministry ruled recently the term Allah -- long used by Christians in Malaysia to refer to God -- could no longer be used by non-Muslims.
"Malaysia is probably the only nation where the term Allah by Christians to refer to God is prohibited," parliamentary opposition leader Lim Kit Siang said in a statement, adding that the term was never banned even in the Middle East.
"The term Allah was used to refer to God by Arabic-speaking Christians before Arabic-speaking Muslims existed," he said.
The government clampdown could force Kuala Lumpur-based "Herald - the Catholic Weekly" newspaper to lose its publishing permit if it failed to drop the word Allah in its publication, the publisher said.
The publisher, the Archbishop of Kuala Lumpur, said on Thursday it had filed a lawsuit challenging the state order.
"We are of the view that we have the right to use the word Allah which right is now sought to be curtailed," his office said in a statement. "We have decided to have our legal position to use the word to be determined by the courts."
Politically dominant ethnic Malay Muslims form about 60 percent of the population of roughly 26 million, while the ethnic Indian and Chinese minorities include Hindus, Buddhists and Christians.
Political analysts say the ruling is an extension of the Malay Muslim supremacy taking firmer root in Malaysia.
"The Malays want to make Islam exclusive to Muslims," said one analyst.
Separately, another church group, the Evangelical Church of Borneo in the eastern Malaysian state of Sabah, has filed a suit against the ministry's move to stop it from importing Christian books which contain the word Allah.
"From the earliest days of the church, the Malay-speaking congregation of the Church have been freely using the Alkitab, the Bahasa Indonesia translation of the Holy Bible wherein the word Allah appears," it said in the suit.
"The Christian usage of the word Allah predates Islam," it added.
A spokesman for Deputy Internal Security Minister Johari Baharum said he could not comment because the cases were before the courts.