Kuala Lumpur, Malaysia (CNN) -- Malaysian opposition leader Anwar Ibrahim goes to trial on Tuesday to face a sodomy charge that he has decried as politically motivated.
It is the second time that Anwar, one of Asia's best-known opposition leaders, has been charged with offenses that include sodomy.
Investigators arrested Anwar in July -- four months after a loose coalition of opposition parties he led made gains on the ruling party in parliamentary elections.
The charge alleges that he sodomized a 23-year-old aide. Anwar has pleaded not guilty to the charge.
"I don't believe that I'm going to get a fair trial," Anwar told CNN Monday. "A fair trial would require a competent, independent judge to immediately strike out the charge because any sexual assault must have a case to support the charge."
The charge carries a maximum sentence of 20 years in prison and a whipping, according to the Malaysian National News Agency.
Anwar has called his arrest a "dirty trick and conspiracy" orchestrated by authorities who are trying to discredit him.
"They think that by doing this they can frustrate the opposition because they think the coalition will be more fragile without me," said Anwar, who oversees a multi-ethnic opposition alliance and his own Justice Party. "Clearly they have underestimated the commitment of the (parties)."
The U.S. State Department has said that Anwar's arrest "raises serious questions and concerns."
Anwar was the heir apparent to former Prime Minister Mahathir Mohamad until 1998, when he was sacked and charged for corruption and sodomy. Anwar spent six years in prison after being convicted on corruption charges in 1999 and on sodomy charges involving his wife's former driver in 2000.
Malaysia's highest court overturned the sodomy conviction and ordered him released from prison in 2004. However, the corruption verdict was never lifted, barring him from running for political posts until 2008. A loose coalition of opposition parties -- with Anwar at the helm -- won 82 of 222 parliamentary seats in elections in March of that year. It was the second time in the country's history that the ruling party failed to gain the two-thirds majority needed to amend the constitution.
In the current case, a 23-year-old male aide has accused the 60-year-old Anwar of sodomizing him at a luxury apartment in June. Sodomy, even if consensual, is punishable by 20 years in prison in the majority-Muslim country.
Anwar has said the investigators trying to build a case against him are the same ones who he claims hid evidence that could have cleared him in his sodomy-related conviction in 1999.
Malaysian Home Affairs Minister Syed Hamid Albar has told CNN that politics played no role in the arrest.
"Anwar is not above the law; everyone is within the law," Albar said. "We will look at it purely as a case of criminality that the government needs to investigate."
He said police took two weeks to investigate the sodomy charge before an arrest was made.
"We went slowly, knowing the international community is observing us on this -- knowing his popularity on the international level," Albar said. "To be fair, you must give the complainant the chance that he's being heard. It is the right of a citizen. It is the police's duty to investigate."