During the interwar period, Lens experienced a time of intense trade union activity. The trade union movement in the mines of the Pas-de-Calais dated back to 1884. The central administration of the Pas-de-Calais Miner's Union located in Lens at the Miner's Union Office (built in 1911 and rebuilt in 1922). One local figure left his mark on the history of the mine's trade unionism: Emile BASLY (mayor of Lens from 1900 to 1928). In 1891, Emile BASLY was appointed chairman of the Pas-de-Calais Miner's Union. He became a member of parliament in 1891. Along with the other "miner MP", Arthur LAMENDIN, he passed several important bills, on relief funds (26th June 1894), pension funds (29th June 1894) and workplace accidents (1898). During the interwar period, the trade union movement was affected by the debates between "unitarians" and "reformists". In 1921, they split up at the Lille congress. But, the reformists and unitarians created a new union in 1935 to guarantee the triumphant success of the Popular Front at the legislative elections held in 1936. There then ensued the strikes during which some pits and factories were picketed resulting in the Matignon agreements.