Mr Anwar is a key figure in a resurgent Malaysian opposition
Malaysian opposition leader Anwar Ibrahim has asked an Islamic court to investigate a former aide, who accuses him of sodomy, for alleged slander.
Under Islamic law, anyone making accusations of a sexual crime, such as sodomy, has to produce four witnesses to back up their claim.
Mr Anwar says the sodomy allegation is a "conspiracy" by the authorities aimed at ending his political comeback.
The government in Kuala Lumpur denies any involvement.
If Mr Anwar's male accuser is found guilty of making a false allegation, he could be jailed for up to three years and fined.
Mr Anwar, a former deputy prime minister, is being investigated by police over the sodomy claims - a crime punishable by up to 20 years in prison in predominantly Muslim Malaysia.
He was jailed for six years after allegations of sodomy and corruption emerged in 1998. That sodomy charge was later overturned.
On Wednesday, Mr Anwar submitted a complaint against his 23-year-old accuser at the Federal Territory Religious Department in Kuala Lumpur.
"This slander is a major issue particularly because it involves a sexual crime, and the attempt is, of course, to mislead the Muslim population to attack me and my character," Mr Anwar told reporters.
"It's demeaning to me and my family," he said.
Under Islamic law, anyone who alleges unlawful sex must produce four credible male witnesses to back their claim, Mr Anwar's lawyer said.
"Otherwise, they cannot allege. It's a very serious allegation," lawyer Ainiah Kamaruzaman said.
Mr Anwar has also filed a defamation suit at a civil court.
On Monday, Mr Anwar's accuser, who has been under police protection since he made the claim in June, made his first public comments on the sodomy case.
"The truth will prevail. Falsehood will surely be exposed," the accuser was quoting as writing in an e-mail by the Star newspaper.
Malaysia has a dual court system. Islamic courts consider civil matters relating to Islam, while civil courts decide issues not related to the religion.
Mr Anwar had appeared a spent political force before his three-party opposition alliance made a strong showing in March polls.
Once the deputy and presumed successor to former Prime Minister Mahathir Mohamad, Mr Anwar was sacked to face charges of sexual misconduct in 1998 and went on to serve six years in jail for sodomy and corruption.
The sodomy count was later overturned, and a ban on public office relating to the corruption conviction expired in April.
Mr Anwar has filed complaints against police chief Musa Hassan and attorney general Abdul Gani Patail over his sodomy trial in 1998. He accuses the two men - then respectively the police investigating officer and prosecutor - of faking evidence against him.