The general secretary of the Unite union has written to the Prime Minister on the fortieth anniversary of the 'Shrewsbury 24' trial, calling for a review.
Six workers, including the actor Ricky Tomlinson, were jailed in 1972 for their trade union activities.
They had been picketing construction sites in Shrewsbury in support of a nationally called builders strike.
Len McCluskey said: _“It was forty years ago today (3 October) that 24 construction workers were put on trial in Shrewsbury for their trade union activities.
“The workers have been protesting their innocence ever since and are progressing an application to the Criminal Cases Review Commission."