He joined the Transport and General Workers' Union (TGWU), and sat on the unofficial Joint Shop Stewards' Committee, through which he became an ally of Jack Jones.
[1] In 1970, Greendale was elected to the National Executive of the TGWU, in which role he sought to help the union keep pace with industrial developments, such as containerisation, expand the National Dock Labour Scheme to include all ports, and build solidarity with unions in other industrial sectors.
[1] In 1986, The Sun newspaper ran a campaign against Greendale, publishing a front-page story with the headline "The Commie Grip Inside Britain's Biggest Union", alleging that he manipulated the results of union elections.
[5] He expected to lose his job as a result but, after the national strike was called off, his fellow shop stewards secured his continued employment, by threatening a walk-out if he was not kept on.
[1] Greendale was re-elected to the union's national executive in 1990,[6] but by this time was focusing on local politics.