(CNN) -- Brazilian public notary Claudia do Nascimento Domingues set off a firestorm by granting Brazil's first civil union to a trio, an act so unprecedented that there isn't a word for it in Portuguese.Uniao poliafetiva is the label she created. "Polyfidelitous union" is her best guess in English.
The relationship involves three professionals in their 30s -- one man and two women -- who, she says, live together, love one another as equals and are like any other non-married cohabiting couple -- except they are three.
What Domingues did was legally register the trio as a "stable union," a civil union that extends all of the benefits of marriage, though there is debate about what rights the threesome will actually enjoy. It short, it recognizes the trio as a family entity for public legal purposes.
Domingues has not released the identities of the three.
But not all are embracing the unique alliance.
"This union is void of any legality," said Regina Beatriz Tavares da Silva, head of the family law committee of a lawyers' association in Sao Paulo.
Brazilian law defines marriage as a union between two people, so it is impossible for a civil union of three to be granted the rights of a marriage of two.
"It goes directly against the constitution," da Silva said. "Monogamy is defined as relations between two, not three or four or five."
The first-of-its-kind civil union has led to an outcry from religious groups, too. Those who fear the "slipperly slope" feel the ground moving underneath their feet.
"The institution of family cannot be defended with the approval of actions that seek to distort its definition," the religious, conservative Plinio Correa de Oliveira Institute said in a statement. "The purpose of this (union) is not to build families, but to destroy them."
The controversial civil union "is proof that there is a plurality of familiar relations, though not all deserve judicial or legal standing," Rolf Madaleno, director of the Brazilian Institute for Family Law, said in a statement. "The action carried out does not provide protections and does not confer rights."