Until the Trade Union Act of 1871, it was still illegal to organise or even take part in a trade union, as it was thought to disrupt the free course of trade. A Combinations of Workmen Act had been passed in 1824, which repealed earlier punitary Acts, but this led to an outbreak of strikes across the country. The government responded by passing the 1825 Act, which imposed criminal proceedings again for such actions as picketing, which encouraged other workers to refrain from work.
Editors. "Combinations of Workmen Act". The Literary Encyclopedia. First published 30 August 2013
[http://www.litencyc.com/php/stopics.php?rec=true&UID=204, accessed 30 March 2017.]