In 1972 there was a national strike of building workers.
Following the strike, 24 of the workers were tried in Shrewsbury accused of violent crimes.
The trial resulted in six of the pickets being jailed and 18 others receiving suspended sentences. Three pickets were given extra terms for conspiracy using a law from 1875.
Ever since the pickets were released efforts to overturn the verdicts and hold a public inquiry into the role of the government and employers have been ongoing.
On 12 March there will be a lobby of parliament at 12 noon.