The grand justices of Taiwan's Constitutional Court will reveal their decision on the constitutionality of the country's same-sex marriage ban on May 24, the secretariat in Taipei said on Monday.

The 14 justices heard the case of gay rights activist Chi Chia-wei and consulted attorneys and government officials over whether the Civil Code's description of marriage as between a man and a woman contravened the Constitution's guarantee that "all citizens, irrespective of sex ... shall be equal before the law."

If the justices rule in Chi Chia-wei's favour, same-sex marriage would be immediately legalized, making Taiwan the first country in Asia to do so.

The decision would override a same-sex marriage bill currently working its way through the country's legislative Yuan after being proposed in December by the ruling Democratic Progressive Party.

Observers believe another outcome would see the justices ruling that the ban is not unconstitutional, but advising the government to introduce a unique law for same-sex unions.

Activists have cautioned against such a law, warning that it would degrade same-sex couples to second class citizens.