SINGAPORE - An activist for lesbian, gay, bisexual and transgender (LGBT) rights, who is a retired general practitioner, has filed a new court challenge against Section 377A of the Penal Code, a law that criminalises sex between men, arguing that it is unconstitutional.

Dr Tan Seng Kee, 61, better known as Roy Tan, was the main organiser of the first Pink Dot event in 2009 advocating LGBT rights.

He is represented by lawyer M. Ravi from Carson Law Chambers, who filed the case in the High Court last Friday (Sept 20).

The Attorney-General (A-G) has been listed as the defendant.

Section 377A of the Penal Code criminalises acts of "gross indecency" between men and the offence carries up to a two-year jail term.

In court documents seen by The Straits Times, Dr Tan stated that Section 377A is inconsistent with Article 9 of the Constitution, which states that no person shall be deprived of his life or personal liberty save in accordance with law.

He also stated that Section 377A is inconsistent with Article 12, which states that all persons are equal before the law and entitled to its equal protection, and Article 14, which states that every citizen of Singapore has the right to freedom of speech and expression.

Dr Tan said in a statement on Wednesday (Sept 25) that the challenge is based on "novel arguments".

For example, the Public Prosecutor has discretion on whether or not to prosecute an accused person under Section 377A and the Government has said that the law will not be enforced against acts done in private, Dr Tan said.

He added that this is incongruous with Section 14 of the Criminal Procedure Code, which requires the police to unconditionally investigate all complaints of suspected arrestable offences.

"This subjects gay men to the potential distress of an investigation into private conduct where they have a legitimate expectation that the state will decline to prosecute," Dr Tan said in his statement.

"It represents not only a contradiction between the Public Prosecutor's prosecutorial discretion and the non-discretionary carriage of criminal justice on the ground but is also a restriction on their personal liberty, which is not consistent with Article 9(1) of the Constitution."

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Dr Tan said he will also submit as evidence arguments derived from comments on the "constitutionally unsatisfactory status quo" by former A-Gs V. K. Rajah, Walter Woon and Chan Sek Keong, as well as current Deputy A-G Hri Kumar Nair.

A pre-trial conference has been set for Oct 8.

The case will challenge the Court of Appeal's previous ruling in 2014 that Section 377A is constitutional.

The three-judge Court of Appeal had then rejected two separate challenges by Mr Tan Eng Hong, who was also represented then by Mr Ravi, and a gay couple, Mr Gary Lim and Mr Kenneth Chee.

The highest court in Singapore has upheld Section 377A of the Penal Code, rejecting arguments that the provision contravenes the Constitution.

The court held that Section 377A did not violate Article 9 as the phrase "life and liberty" referred only to the personal liberty of a person from unlawful incarceration and not to the right of privacy and personal autonomy.

As for Article 12, the court held that Section 377A passed a test used by the courts in determining whether a law complies with the constitutional right of equality.

In Singapore, the courts have used the "reasonable classification test" to determine whether a statute that differentiates is consistent with Article 12.

Under this test, a statute that differentiates is constitutional if the classification is based on an "intelligible differentia" – a discernible distinguishing feature shared by those who are treated differently – and if the differentia bears a rational relation to the objective of the law.

The court held in 2014 that the classification prescribed by Section 377A - men who perform acts of gross indecency with other men - was based on an intelligible differentia.

The court also ruled that Section 377A fell outside the scope of Article 12, which forbids discrimination of citizens on grounds including religion, race and place of birth. The court observed that Article 12 did not contain the words "gender", "sex" and "sexual orientation", which related to Section 377A.

In his statement, Dr Tan said the court had erred in ruling that Section 377A passed the test and disputes that the law is based on an intelligible differentia.

He said acts of "gross indecency" may take place between men only, women only and a mix of men and women, but "such acts cannot be meaningfully distinguished across the three classes".

"However, Section 377A only proscribes acts between males. There is therefore no intelligible differentia as Section 377A is intended to proscribe acts of gross indecency,” said Dr Tan.

Two other constitutional challenges against Section 377A are currently before the courts.

One was filed by Mr Bryan Choong in November last year. Mr Choong is the former executive director of Oogachaga, a non-profit organisation working with the LGBT community.

Another was filed in September last year by disc jockey Johnson Ong Ming, who goes by the stage name DJ Big Kid, shortly after India's Supreme Court struck down a similar law.

The Indian court's decision sparked renewed debate on Section 377A here.

In August last year, businessman Ho Kwon Ping questioned the need for Section 377A in a public talk. Barely a month later, veteran diplomat Tommy Koh wrote on Facebook urging the gay community to bring a class action to challenge the constitutionality of Section 377A.