Nov. 18 (Bloomberg) -- Japan’s lower house approved an amendment to the country’s nationality law that may allow thousands of mixed-race children to become citizens.

The change, which the upper house must approve, applies only to out-of-wedlock children of Japanese fathers and non-Japanese mothers. Under the new law children will be able to claim citizenship for up to 20 years after they’re born; current legislation requires a Japanese father to acknowledge the child while it’s in the womb.

As many as 20,000 children living in Japan may be eligible for citizenship after the change, said Yasuhiro Okuda, a law professor at Chuo University in Tokyo who has followed the case. Still, the legislation enforces the notion that heredity and not birthplace determines Japanese citizenship, he said.

“It cements the idea that nationality is based on blood,” Okuda said. “The law does nothing to broaden the definition.”

Today’s vote comes five months after the Supreme Court ruled previous legislation was unconstitutional. The new law includes a penalty of up to one year in prison for filing a false claim.

“This opens the door to possibly hundreds of thousands of false claims,” Akira Momochi, a Nihon University professor who opposes the law, said of the change. “It’s an insult to the dignity of Japanese citizenship.”

The Supreme Court ruling focused on the case of 10 children living in Japan who were born out of wedlock to Filipino mothers and Japanese fathers. Since the ruling, the government has received 112 citizenship applications, according to the Justice Ministry.

To contact the reporter on this story: Toko Sekiguchi in Tokyo at Tsekiguchi3@bloomberg.net

Last Updated: November 17, 2008 23:59 EST