http://ec.europa.eu/social/main.jsp?catId=1143&intPageId=3193&langId=en/
https://www.etuc.org/fr/presse/rien-quen-2017-chaque-travailleur-subi-une-perte-de-salaire-de-1764-€-en-raison-de-la#.WqrAWUxuI2x
https://www.ilo.org/legacy/english/inwork/cb-policy-guide/declarationofPhiladelphia1944.pdf
http://www.congreso.es/consti/constitucion/indice/titulos/articulos.jsp?ini=155&tipo=2