A group of parents plans to sue the government next month over what it says is an unfair sole custody system, claiming that it violates their right to raise children after a divorce.

The 12 men and women from eight prefectures, including Tokyo, Nagano and Kyoto, argue that the system, which allows only one parent to have custody after a divorce under the Civil Law, infringes the Constitution's guarantee of equality under the law.

The plaintiffs, who will file the suit seeking damages at the Tokyo District Court in late November, are parents who have faced difficulties becoming involved with their minor child or children after separating from their partner.

They established the group to seek a joint custody system and to proceed to file the lawsuit calling for a revision that would introduce such a system, granting joint custody to both divorced parents, as well as those who were de facto married.

Under the current system, joint custody applies only to parents who are married.

According to the attorney representing them, the group lawsuit over joint custody for separated parents will be the first such suit to be filed in Japan.

Problems with the current system have been pointed out, such as intense tug-of-wars between divorcing parents over custody and the lack of communication between noncustodial parents and their kids.

Under the Civil Law, at the time of a divorce, rules are set for meetings between a noncustodial parent and a child, but there is no penalty if the rules are ignored.

However, some people oppose a joint custody system, because it would make it more difficult for a mother or father suffering from domestic abuse by a spouse to escape the situation.

A 54-year-old man from Tokyo, who plans to join the suit, divorced his wife about 11 years ago when their son was one and a half years old. The family court set his visitation rights for three times a year, but he was denied the opportunity.

"I would like to voice my criticism of the sole custody system at the trial," he said.

A similar lawsuit was filed by 14 people seeking compensation in March last year, claiming that the government failed to enact legislation on visitation rights by divorced parents.

The Justice Ministry is scheduled to set up an experts panel as early as this year to discuss whether to introduce a joint custody system that would apply after a divorce.