A group of 12 people in Japan plan to file lawsuits next month to challenge the constitutionality of legal provisions requiring married couples to use the same surnames.

Their lawyers say calls for the use of separate surnames are growing louder even though the Supreme Court has found the provisions constitutional in two previous rulings.

The 12 people are five common-law couples and one married couple, who live in Tokyo, Hokkaido, Nagano Prefecture and elsewhere.

They say the Civil Code and family register law provisions that do not allow married couples to have separate surnames violate the Constitution that guarantees freedom of marriage and are thus invalid.

The would-be plaintiffs and their lawyers say losing one's birth name makes it difficult to maintain credibility and evaluations linked to the old name. They say quite a few people feel like they are losing their identity.

They also say those who have chosen common-law marriage to keep their separate surnames often face disadvantages as a result.

They plan to file group suits with the district courts in Tokyo and Sapporo on March 8, seeking compensation from the state.

Similar lawsuits have been filed in the past. In 2015 and 2021, the Supreme Court's 15-member grand bench upheld the provisions as constitutional in majority rulings. But five justices in 2015, and four in 2021, gave a minority opinion that they are unconstitutional.

The lawyers are calling for a change in the top court's judgment, noting that Japan's largest business lobby and many local assemblies support separate surnames.

The Japan Business Federation, or Keidanren, says married couples should be allowed the choice of keeping separate surnames.

Its diversity promotion panel has asked Gender Equality Minister Kato Ayuko to introduce an option for separate surnames.

In 1996, a government panel proposed that couples should be allowed to decide whether to have a single family name or separate surnames.

Keidanren Chairman Tokura Masakazu has urged the government to push for the change as a top priority to support workstyle reform for women. He said he does not know why it has taken such a long time.