Peeved by the new status of the French Interior Minister, Nicolas Sarkozy, as a best-selling author, the country's Socialists say he is unfairly using his book to start his presidential campaign.
In the three weeks since publication of Témoignage (Testimony), which sets out Mr Sarkozy's political thoughts, the book has sold more than 200,000 copies and is in its sixth print run. It tops the sales list of the Fnac chain, outselling such favourites as Marc Levy and Mary Higgins Clark.
Yesterday, François Hollande, the Socialist first secretary, demanded "full transparency" over the book and over the financing of a promotional tour by Mr Sarkozy's UMP party.
But Yves Jégo, the UMP national secretary, said the book fell within the rules of French campaign funding, in which candidates' campaign budgets are set by the constitutional council.
"We're totally within the law," said Mr Jégo. "... we have had not any promotional costs. All the negative publicity by the political establishment has given the book an enormous free plug."
At the weekend, Le Monde newspaper said the constitutional council would scrutinise the spending by the publisher, XO Editions, on the production and promotion of Mr Sarkozy's book.
But Mr Jégo said Mr Sarkozy had not yet been selected as a candidate for the presidential elections set for next April.
For the Socialists, Mr Hollande is unlikely to take his criticism further. His partner, Ségolène Royal, is among the favourites of the potential socialist candidates. And she is also planning a book.