Syprolux is the official union for all railway jobs in Luxembourg, so mostly relevant if you work for CFL or any of their subsidiaries.  Founded in 1922 the union is already existing for more than 100 years and like every union they are negiotationg about work conditions with the employeers in this case mostly CFL. Members also benefit from support on their tax declaration, job related legal insurance, acces to complementary health insurance CMCM and couple of more things. As of now the website is only available in German. Their offices are located close to Luxembourg main station (what a suprise) at 20 A Rue de Strasbourg, 2560 Gare Luxembourg. You can also reach the administration at syprolux@pt.lu