Rhondda, and nearly half of the men did not go in to work. Mainwaring did get the South Wales nomination for the secretaryship of the Miners' Federation of Great Britain in 1932, after the death of A. J. Cook. A preferential voting system was used, and Mainwaring came in third place on first preference votes, being eliminated from the voting. Rhondda East byelection The death of Lieutenant-Colonel David Watts-Morgan, the Labour Member of Parliament (MP) for Rhondda East, in early 1933 left a vacancy for a Labour candidate in which the influence of the miners was predominant. Mainwaring's name was immediately mentioned as a possible candidate, with rivals including Alderman David Lewis, Mrs Watts-Morgan (the widow of the former MP), and some local party figures. Mainwaring was selected, and faced opposition from Arthur Horner of the Communist Party and William Thomas, a local Liberal, in the byelection. Mainwaring received a letter of support from Labour Party leader George Lansbury, and an appeal from the President, vice-president and General Secretary of the South Wales Miners' Federation was made for all miners and their families to vote for him. The Labour Party had won easily in a straight fight with Arthur Horner at the previous election, but the decision of the Liberal Party to fight an energetic campaign (the Liberal candidate was allied with David Lloyd George and opposed to the National Government) was thought to have given the party a scare because Labour had benefited from Liberal votes in 1931. Mainwaring predicted that he would get between 20,000 and 22,000 votes. In the event, Mainwaring won with 14,127 votes, with Horner second having increased his vote compared with 1931. Parliament In Parliament, Mainwaring concentrated on mining issues, calling in July 1933 for the Home Secretary to examine the circumstances of the Bedwas colliery dispute where miners and their families had been imprisoned for breaches of the peace. He moved the rejection of the government's Coal Mines Bill in 1934, arguing that legislation dealing with coal mines was futile while the mines were in private ownership, and had evaded previous acts. He was also active on issues affecting the unemployed, where he consistently opposed attempts to reduce unemployment benefit; in 1935 he warned that agitation on the subject in South Wales would "spread like a flame throughout the country". Arms industry During the 1930s he was a pacifist, criticising private armament firms