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The space astrometry mission GAIA will construct a dense optical QSO-basedcelestial reference frame. For consistency between the optical and radiopositions, it will be important to align the GAIA frame and the InternationalCelestial Reference Frame (ICRF) with the highest accuracy. Currently, it isfound that only 10% of the ICRF sources are suitable to establish this link,either because they are not bright enough at optical wavelengths or becausethey have significant extended radio emission which precludes reaching thehighest astrometric accuracy. In order to improve the situation, we haveinitiated a VLBI survey dedicated to finding additional high-quality radiosources for aligning the two frames. The sample consists of about 450 sources,typically 20 times weaker than the current ICRF sources, which have beenselected by cross-correlating optical and radio catalogues. This paper presentsthe observing strategy and includes preliminary results of observation of 224of these sources with the European VLBI Network in June 2007.

VLBI observations of weak extragalactic radio sources for the alignment of the future GAIA frame with the ICRF