During the period up to 1931, industrial relations had already deteriorated as manifested by a number of short-duration strikes over pay and the efforts of the South Wales Miners Federation to obtain recognition at the mine. In the years of 1931 and 1932, coal production throughout the country declined, exacerbating the ill-feeling. During strikes in 1933 the existing workforce was shut out en masse and the Colliery Management toured the Labour Exchanges of South Wales to recruit unemployed miners in their places. There were plenty of willing replacements during these days of high unemployment and those less-willing faced losing their dole if they turned down a job at Bedwas. Men were recruited from as far away as Brecon and Sennybridge, Cwm and Llantwit Vardre. The GWR laid on special trains from Brecon to Bedwas to cover every shift. It was joined by another from Llantwit Vardre travelling via Pontypridd and the Machen loop, from where the train was shunted up the valley to Bedwas. As many as 700 men were brought in by train for each shift. As the first collier reached the colliery offices, the last would be leaving Bedwas Station.
Other men such as the existing pumpsmen continued working and were dubbed as 'blacklegs'. (As there were no pithead baths in those days, those who had broken a strike could be identified, even if they had washed their hands and faces, by the coal dust on their legs.) Several homes were attacked and buckets of black tar thrown through the windows. 'Blacklegs' were attacked, doused with urine and then covered in feathers in a familiar ritual. Large numbers of pickets were stationed at all entrances to the colliery and in fact joined by considerable numbers of the general public. The Colliery company responded by the erection of two wooden barracks adjacent to the lamproom where 50 or so members of the Monmouthshire Constabulary were stationed under the command of Superintendent Spendlove.
Matters came to a head on 17th March 1933, when a Mr. Jack Davies, one of the 'blacklegs' was being escorted to his home in Navigation Street, Trethomas. Mr. Davies walked with the aid of a walking stick, having only one leg. He was surrounded by mounted Police and a crowd was shouting abuse. Suddenly, part of a brick thrown from the crowd hit Mr. Davies in the side of the head and he collapsed. Several officers went into the crowd and arrested a Mrs. Fred Ludlow and Mrs. Ludlow, whom it was alleged had thrown the brick with such accuracy. The Police escorted the two ladies to Bedwas Police Station, about a mile away from Trethomas, but they were followed every inch of the way by an angry procession led bt the SWMF Lodge Secretary, Billie Wilson and other SWMF members.
A large contingent of officers guarded the Police Station and were surrounded by a large, hostile crowd, which clearly had the intention of freeing the two ladies inside. Appeals were made by the Police for the crowd to disperse, with no effect. After a while, a Bull-nosed Morris Oxford appeared through the crowd which carried a local Justice of the Peace, Mr Edgar Lewis. After speaking with Supt. Spendlove, he read the Riot Act, following which the Police waded into the crowd, hitting out in all directions. The crowd was dispersed and within a few minutes Church Streeet was occupied only by those with injuries caused during the fracas. The two ladies later stood trial and were both sentenced to imprisonment, as were nine others, including Lil Price, who was sentenced to six months for assaulting a Police Officer.
The 1933 strike continued for some time. Some colliers resorted to reopening the former drifts and levels in Trethomas woods to get coal. Gleaning coal from the waste tips was another common activity. However, the end of the strike did not see the return to work for many. The company retained much of the imported labour. To make up the numbers, lists of 15-16 names of former colliers were put up weekly at the colliery offices until a full complement was reached. Most colliers were not taken back on and many emigrated to 'Little Wales' in Slough, Berkshire. Many families moved into the area, but relations between the former and new miners and their families were tense. An example was that the new miners had their own social club near the colliery - the Ruperra Club.
With the SWMF banned, the colliery company entered into an arrangement with a Nottingham-based Union - the Miners Industrial Union or 'Spencers Union' - membership of which became a condition of employment at the colliery.
The attempt to obtain recognition of the SWMF at the mine became a major focus of the labour movement in South Wales. Eventually, following a prolonged stay-in strike below ground in the North Pit in 1936 the SWMF was recognised. This effective tactic recognised that a strike could not be broken by the usual response of bringing in blacklegs, if the underground workings were occupied. Over 40 miners stayed underground in this famous strike for over 54 hours.
In the late 1930's, the recession gradually ended and with the threat from Nazi Germany, the requirement for steam coal was enormous. The long-standing industrial relations problems started to ease and in 1939, 675,000 tons of coal was raised, by 1,850 men, the all-time record for the pit.