Asked to comment on this latest move to revamp the rules governing the EU's Schengen border free space, a European Commission spokesperson yesterday (19 April) avoided a direct reply on the grounds that the letter had not yet been received.
The German daily Süddeutsche Zeitung widely quoted the letter, signed by French Interior Minister Claude Guéant and his German colleague Hans-Peter Friedrich.
The ministers claim their nation's right to re-establish controls if an EU member state fails to control illegal immigration.
For the time being, Schengen member countries can only briefly establish border controls, for events such as football matches and high-level international meetings, to prevent hooliganism or violent protests.
But this time the proposal is obviously aimed at longer-term measures, and the country targeted is clearly Greece.
French President Nicolas Sarkozy, who faces a difficult attempt for re-election, has vowed to pull his country out of the EU's border-free Schengen area unless the treaty rules are changed so that decisions are made by nations and not "technocrats and courts".
Sarkozy has repeatedly called the Greek-Turkish frontier "a sieve" and said that a country that has difficulties controlling its borders should be excluded from Schengen.
The Greek-Turkish land border that spans 130 kilometres is secure except for an area of around 20 kilometres near Orestiada and the Turkish city of Edirne, at the place where the river Evros (in Greek, Meriç in Turkish, Maritsa in Bulgarian) crosses the border.
In Brussels, the European Commission downplayed the issue, saying the number of migrants crossing the Greek-Turkish border had decreased from 2,000 to 500 a week.
How far the Franco-German letter can be interpreted in the French election context remains unclear. Germany too has warned Greece that it should tighten its borders, and has expressed positions that Schengen rules should be strengthened with more powers given to member states.
Legally, it is difficult, if not impossible, to exclude a Schengen member state from the agreement. But the implications of re-introducing border controls with Greece could affect Bulgaria and Romania's bid to join Schengen, which is officially opposed by the Netherlands.