Authorities in south-west France have told a mayor not to go ahead with plans for the country's first gay marriage.
Mr Mamere had offered to marry gay couples earlier this month
Noel Mamere, mayor of the Bordeaux town of Begles and a leading member of parliament for the Green Party, had said he would conduct the marriage.
But the public prosecutor of Bordeaux has declared his opposition and ordered Mr Mamere to abandon his plans.
The wedding plans have sparked public debate, drawing condemnation from the government and church leaders.
The mayor had said he would perform the marriage of Bertrand Charpentier and Stephane Chapin on 5 June.
He said there was nothing in French law to prevent it, and that it was unacceptable that gays did not have the same rights as other French citizens.
Civil unions between same-sex partners have been legal in France since 2000.
However, gay lobby groups say these fall short of legal marriages as they do not come with benefits such as adoption rights or the same fiscal advantages.
But public prosecutor Bertrand de Loze has now sent a fax to the mayor, saying: "In your capacity of civil servant, you are hereby forbidden from celebrating the planned marriage.
"As an officer of public authority, it is important that you refrain from any initiative designed to undermine the application of the law."
French Justice Minister Dominique Perben has expressed his opposition to the marriage and told parliament last month that he intended to ask the Bordeaux prosecutor to block the marriage.
The Roman Catholic Archbishop of Bordeaux, Jean-Pierre Ricard, has condemned the plans not only on religious grounds but also as a means "to support the founding principles of social life itself".
Same sex civil marriages are allowed in the Netherlands and Belgium. Some other European countries, like France, allow only civil unions.
The new Spanish Prime Minister, Jose Luis Rodriguez Zapatero, has said he is in favour of allowing same-sex marriages.