The spring 2010 mass demonstrations in Greece, against the austerity plans imposed by the national government, point to certain new features of collective action for trade-union mobilizations. Here, we profile the conditions and the content of these mobilizations, and analyse the latter, aiming to show that they are forms of social protest which Tarrow calls a ‘mobilization phase of a cycle of contention’. We argue that these forms have enabled social movement actors to overcome – even temporarily – the historically rooted basic weaknesses of organization, collaboration and co-ordination in the Greek trade-union movement.