The Republic's department of foreign affairs has refused to say if it issued adoption visas to 11 Irish couples caught up in a Mexican "babies for sale" scam.
The couples are being questioned after seven children -- aged from two months to two years -- were taken from them after police smashed an international child-smuggling ring. Although they are helping police with their inquiries, they have not been arrested.
Mexican authorities want to find out how much the couples knew about the illegal trade after arresting three Mexican women.
The three, who are in their 30s, are accused of buying the infants from their mothers through newspaper advertisements, before handing the children over to the couples.
Police say they have not ruled out the possibility of further arrests. The Adoption Authority of Ireland confirmed last night that prospective parents must apply for adoption visas from the Irish Department of Foreign Affairs under official legal procedures.
This is one of the rules that must be followed by those wishing to adopt along with other regulations set out under the Hague Convention, which has been ratified by both countries.
When asked about the visa issue last night, a spokesman for the Department of Foreign Affairs said: "We do not give out that information."
The Adoption Authority said adoption visas from the Irish authorities are a mandatory requirement for Mexican adoptions, while parents must also obtain special clearance certificates after being vetted by the HSE.
Chairman Dr Geoffrey Shannon said an "updated notice" issued by the authority last week warned prospective parents they should "not enter into any private arrangements with private individuals or private agencies" to secure a Mexican adoption.
The notice also said children under five should not be proposed for adoption, bar those with special needs or siblings.
"In terms of red flag issues, our advisory note highlighted that prospective adoptive parents must state the purpose of their visit when going to Mexico, and obtain an adoption visa," he said.
He said it "would not be appropriate" to say whether the group in Mexico had been in touch with the authority, although he confirmed this is part of official procedure.
However, Susan Lohan of the Adoption Rights Alliance, which represents adopted people, accused the authority and the Department of Foreign Affairs of "turning a blind eye" to illegal adoption.
"This shouldn't be a surprise to anybody when there are corrupt foreign officials and desperate wealthy westerners," she said.
"The really big question is why successive governments and the authority won't touch this whole area of illegal adoption with a bargepole. Even the dogs on the street know it goes on.
"It's about finding homes for children, not finding children for homes. God love those children who will find out in 20 years' time they were trafficked," Ms Lohan added.
The children rescued at the weekend are now in state care.
The Irish couples, none of whom have been named, were questioned in Guadalajara, the capital of the Mexican state of Jalisco, at the weekend.
As well as the seven babies seized from them, another two babies were rescued during a fourth arrest.
The Irish couples said they were living with the children as they had been told this was part of the process before adoption. It was unclear last night how, or whether, it was planned to bring the children into Ireland.
The couples are believed to have been given the babies at a hotel in Guadalajara and sent to the nearby town of Ajijic.