The Famiee Project said it wanted to spur change by tapping into growing business support for LGBT+ rights in socially conservative Japan and aims to sign up 100 businesses by the time it launches the scheme in July.

Gay marriage is illegal in Japan and although about two dozen cities, towns and wards issue same-sex partnership certificates, they lack legal standing and prejudice persists.

"If we have a big network of corporations that support us, we can persuade the government to change the law," said Famiee Project founder Koki Uchiyama.

"That kind of movement is already happening in Japan," he told the Thomson Reuters Foundation by phone from Tokyo, referring to the growing business support for LGBT+ rights.

The scheme has so far been endorsed by 17 companies including banking firm Mizuho Financial Group, insurer Sompo Japan and Hotto Link, a public-listed data firm where Uchiyama is the chief executive.

Some of the 17 firms have already recognized certificates issued by local authorities, but these documents can only be used in the area they are issued.

Famiee Project said its digital certificates will use blockchain technology and QR codes for record and verification, making it easier for nationwide use.

The project aims to get 100 companies on board by July to provide same-sex couples with benefits such as marriage or parental leave.

It also wants the firms to accept the certificates for services such as opening joint bank account or naming insurance beneficiaries.

The Justice Ministry and Welfare Ministry did not respond to a request for comment.

Japan's laws on LGBT+ issues are relatively liberal compared with many Asian countries, with same-sex relations legal since 1880, but being openly gay remains largely taboo.

About a third of Japanese companies have measures in place to support gay couples, but discrimination is still common, according to Nijiiro Diversity, which campaigns for LGBT+ rights in the workplace.

"This certificate alone is not effective. The government should give more support to companies working towards measures on LGBT+ rights," said the group founder Maki Muraki.

Activist Ai Nakajima said she hoped the scheme would spur government into action.

"Companies are changing, but the government is not changing. So tax benefits or health insurance benefits are still not possible," said Nakajima, who was among 13 same-sex couples to sue the government over the right to gay marriage last year.

Japan's ruling Liberal Democratic Party has said that same-sex marriage was "incompatible" with the constitution, although public polls showing growing acceptance in recent years.