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.

Under the law, the will to obtain non-Japanese citizenship is equivalent to renouncing Japanese citizenship, but the two acts are far from the same, Teruo Naka, the lead lawyer in the suit, told a news conference in Tokyo. The very premise of the law — to prevent citizens from obtaining dual citizenship — is itself constitutionally questionable, he said.

In some cases, people have given up career opportunities overseas that require specific citizenship because of the Japanese system, said Shiki Tomimasu, a lawyer involved in the suit. These people “have been deprived of opportunities to attain greater success” abroad, he added.

“We want people to understand that the current system doesn’t have to be the standard practice,” he said.

Hitoshi Nogawa, one of the eight plaintiffs, moved to Switzerland in 1969 and manages a company there. He obtained Swiss citizenship in 2001, as Swiss citizenship was a requirement for individuals to take part in certain bidding procedures. Nogawa was not aware at that point that acquiring Swiss citizenship meant he would be renouncing his Japanese citizenship.

“Both my parents are Japanese, yet one day I lost my citizenship without any warning. I didn’t have the strength to do anything for about two weeks after hearing what happened,” Nogawa said.

Given how one-sided the whole procedure was, “it was a very painful experience for me,” he added.

As of 2011, 103 of 195 countries allowed their citizens to retain their original nationality while obtaining citizenship from a second country, according to a U.N. report published in 2013. Thirty-seven countries allowed multiple citizenship under specific circumstances, and the remaining 55 banned multiple citizenship.

Six of the eight plaintiffs were forced to renounce their Japanese citizenship upon acquiring non-Japanese citizenship. The other two claim to have lost job opportunities as they gave up acquiring non-Japanese citizenship for fear of losing their Japanese nationality.