The Tokyo District Court on Thursday rejected a damages suit filed by three couples who argued that the country's law forcing married couples to use the same surname is unconstitutional.

The Tachikawa branch of the Tokyo District Court upheld the constitutionality of the relevant provisions of the Civil Code and the Family Register Law in line with a similar ruling by the Supreme Court in 2015.

The plaintiffs, who range in age from their 40s to 70s, sought ¥500,000 each in damages, claiming they have been unable to get legally married as they wish to keep their surnames and have suffered numerous disadvantages as a result.

They said the surname law is no longer rational as society and people's mindsets have changed over time.

In December 2015, the Supreme Court ruled the Civil Code provision was constitutional, saying it treats men and women equally and that the use of a single surname by members of the same family is established practice in Japanese society.

Women conventionally adopt their husband's surname, although the law does not specify which of the partners must give up their surname upon marriage.

Many countries allow the use of separate surnames by married couples and the U.N. Committee on the Elimination of Discrimination against Women has urged the Japanese government to amend the Civil Code.