Three people in a polygamous relationship have been allowed to enter into a civil union in the Brazilian state of Sao Paulo.
The decision has sparked controversy in Brazil. Campaigners in the UK say that tampering with the definition of marriage would pave the way for such unions here.
The Brazilian trio, one man and two women, have been living together for three years.
Public notary Claudia do Nascimento Domingues has sparked controversy by allowing a union between the trio. She says they are entitled to family rights.
But Regina Beatriz Tavares da Silva, a lawyer, said it was “absurd and totally illegal”, and “something completely unacceptable which goes against Brazilian values and morals”.
She told the BBC that the union will not be allowed to remain in place.
The trio’s union was formalised three months ago, but has only recently come to light.
Same-sex unions have been legally recognised in Brazil from 2004, and last year a judge allowed a same-sex union to be recognised as a gay marriage.
News of the polygamous union comes as the Governments at both Westminster and Holyrood consider plans to rewrite the definition of marriage.
A petition against any change, organised by the Coalition for Marriage, has been signed by nearly 600,000 people.
The Coalition commented: “If consensual love between adults is the defining factor as to whether people should be joined in a state-recognised marriage-type union, then there is no logical reason for restricting that union to two people.
“The fact of the matter is, marriage rapidly unravels when politicians start unpicking its established meaning. The Government should stop meddling with marriage.”