Tokyo (CNN) Japan has upheld a law effectively requiring trans people seeking to legally change their gender to be sterilized.

Takakito Usui, a transgender man who wants to change the gender listed on his official documents, had appealed to the court seeking to overturn Law 111 , which requires applicants to "permanently lack functioning" reproductive parts to qualify for gender affirmation.

The Supreme Court unanimously rejected Usui's case Thursday, ruling the 2003 law constitutional -- though judges added it was invasive and encouraged the legislature to review it.

"It is unthinkable in this day and time that the law requires a sex-change operation to change gender," Usui's lawyer Tomoyasu Oyama told CNN.

"When the law was established 15 years ago, LGBT people had to make a bitter decision and swallow the conditions to pave a narrow way for official change of gender. With this decision, I hope lawmakers will change the law to support the wishes of the LGBT community."

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