John Maclean was a Scottish schoolteacher and revolutionary socialist of the Red Clydeside era. He was notable for his outspoken opposition to World War I, which caused his arrest under the Defence of the Realm Act and loss of his teaching post, after which he became a full-time Marxist lecturer and organiser. In April 1918 he was arrested for sedition, and his 75-minute speech from the dock became a celebrated text for Scottish left-wingers. He was sentenced to five years' penal servitude, but was released after the November armistice.

The Clyde Workers Committee was formed to campaign against the Munitions Act. It was originally called the Labour Withholding Committee. The leader of the CWC was Willie Gallacher, who was jailed under the Defence of the Realm Act 1914 together with John Muir for an article in the CWC journal The Worker criticising the First World War.