The law that requires Japanese citizens to give up their nationality if they acquire foreign citizenship is unconstitutional, lawyers leading a lawsuit against the government said Monday.

Eight plaintiffs filed a complaint with the Tokyo District Court on Friday, requesting a judicial decision ruling that the law is unconstitutional, as well as damages for mental suffering related to being forced to give up their Japanese passports.

The clause in the Nationality Law states that Japanese who acquire non-Japanese citizenship of their own will lose their Japanese citizenship automatically. It effectively forbids dual citizenship.