On 6 May, the national student union, the Union Nationale des Étudiants de France (UNEF) – still the largest student union in France today – and the union of university teachers called a march to protest against the police invasion of Sorbonne. More than 20,000 students, teachers and other supporters marched towards the Sorbonne, still sealed off by the police, who charged, wielding their batons, as soon as the marchers approached. While the crowd dispersed, some began to make barricades out of whatever was at hand, while others threw paving stones, forcing the police to retreat for a time. The police then responded with tear gas and charged the crowd again. Hundreds of students were arrested.