Japan should allow married couples to have different surnames, the country's largest business group said Monday, warning that current laws mandating they share a family name cause problems for companies.

Married couples in Japan, where same-sex marriage is not recognised, are required by law to choose either the husband's or the wife's surname -- and lawyers say about 95 percent take the man's.

Maiden names are often kept in the workplace in Japan, but this can cause headaches from reserving hotels to being cited in research papers, which require legal names.

Calls to allow separate surnames have been growing in Japan, with several lawsuits filed over the issue in recent years, but government discussion on the issue has been sluggish.

The Japan Business Federation called on Monday for the government to revise the law banning separate surnames "as soon as possible".

The status quo causes issues for women in particular, the group said, which has around 1,500 member companies and 150 business organisations.

"The surname issue has become a business risk as the number of female senior executives steadily increases," chairman Masakazu Tokura told reporters.

In the lawsuits, plaintiffs argue that requiring married couples to choose one name is against equality under the law and freedom of marriage guaranteed by the constitution.

Couples who choose to stay unmarried face a host of issues, including rights over children, inheritance and tax, they say.

Japan's Supreme Court has twice, in 2015 and in 2021, ruled that the current law is constitutional but it also urged lawmakers to discuss a bill addressing growing calls for flexibility.

Backers of the current laws say having a single family name is important to promote family ties and that efforts to change the rules are an attack on traditional values.