The Michigan Supreme Court heard arguments Tuesday in a dispute over parental rights when a same-sex relationship ends outside marriage.

The American Civil Liberties Union of Michigan said the case could break new legal ground in the state.

"The children of same-sex couples should be able to maintain their relationships with their parents regardless of whether the parents remain together," ACLU attorney Miriam Aukerman said in a court filing.

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Carrie Pueblo is seeking joint custody of a boy who was born in 2008 to her partner at the time, Rachel Haas. Same-sex marriage was not legal in Michigan at the time, but the women had participated in a commitment ceremony in 2007.

They raised the boy together even after their relationship ended. But in 2017, Pueblo said Haas demanded that she stop having contact with the boy.

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Pueblo filed a lawsuit seeking custody, but courts so far have turned her down, saying she and Haas were never married and that Pueblo has no biological connection to the boy.

"Unfortunately Michigan law has not had the opportunity to keep up with the modern family style, with the modern family dynamics, with the modern family composition," Pueblo's attorney, Reh Starks, told the Supreme Court.

Haas' attorney, George Perrett, urged the court to stay on the sideline and let the state Legislature change the law if lawmakers believe it would be appropriate.

"We need a comprehensive approach to this, not a piecemeal approach," Perrett said, noting a variety of consequences since the U.S. Supreme Court in 2015 legalized same-sex marriage.