Six committed same-sex couples, with the aid of the ACLU, sued the state of Montana on July 22, 2010 for failing to provide legal protections for their families in violation of the Montana Constitution’s guarantees of equal protection. The goal of this lawsuit was to see that same-sex couples are able to protect their families with the same kind of legal protections that opposite-sex couples would be offered through marriage.
https://www.aclumontana.org/en/cases/donaldson-guggenheim-v-state-montana