In an open letter, they called for a judicial review of the “absurdly harsh” sentence given to the protesters, three of whom were handed jail sentences.
Simon Roscoe Blevins, 26, Richard Roberts, 36, and Rich Loizou, 31, were imprisoned for up to 16 months after clambering onto lorries bringing drilling equipment to a Cuadrilla site in Lancashire.
The fourth protestor, Julian Brock, 47 was given a 12-month prison term, suspended for 18 months.
Senior representatives from the National Education Union, the Transport Salaried Staffs’ Association (TSSA), the Food and Allied Workers Union and others expressed their concern that the decision would hamper people’s right to take non-violent action against threats to the environment.
“These are by far the longest prison sentences imposed on activists defending the environment since those jailed for the Mass Trespass in 1932,” they wrote.
“It can only be seen as politically motivated in support of a government that has shown it is prepared to ride roughshod over the democratic rights of citizens to achieve an end for which it has no popular support.”
The letter comes after another call for judicial review from hundreds of scientists who echoed the trade unionists’ concerns.
At the recent Trades Union Congress, the trade union movement called for a moratorium on fracking in England following bans in Scotland, Wales and Northern Ireland.
Campaigners said that this decision went against the narrative that fracking should be welcomed because it will create jobs.
Suzanne Jeffery, chair of Campaign against Climate Change trade union group, described the decision made in September as “a political sentence clearly designed to intimidate and stop the anti-fracking movement”.
“It’s important that we as trade unionists stand in solidarity with those who have been jailed.
“Fracking is both unpopular and a risk to our climate – rather than locking up protesters, we need to be urgently investing in good, well-paid, skilled jobs for a low carbon future.”
Manuel Cortes, TSSA general secretary said: “Fracking is a threat to the environment and threatens our communities, workers and water supplies”.
“As trade unionists we support the rights of those seeking to take direct action and we fully back the call for a judicial review in the case of these imprisoned activists.”
On Monday, the UN Intergovernmental Panel on Climate Change (IPCC) released a report detailing the urgent action required to cut global greenhouse gas emissions.
In response, environmental groups such as Friends of the Earth said the government should bring an end to fracking if it wanted to move away from fossil fuels and achieve the kind of cuts outlined by the IPCC.
Fracking remains unpopular among the British public after years of stalled efforts to begin operations.
However, the government has consistently argued for the inclusion of shale gas from fracking in the UK’s energy mix.
When business secretary Greg Clark and housing secretary James Brokenshire announced plans to accelerate fracking development in May, they reiterated the commitment to the “safe and sustainable exploration and development of our onshore shale gas”.
A government spokesperson said: “Shale gas has the potential to be a new domestic energy source, enhancing our energy security and delivering economic benefits, including the creation of well paid, quality jobs. We have been clear that any shale developments must be safe and environmentally sound.”
In response to the sentencing of the protesters, Francis Egan, chief executive of Cuadrilla, said in a statement: “We have always respected the right to peaceful and lawful protest. However, we will continue to condemn unlawful, irresponsible and reckless behaviour that at best inconveniences and costs law abiding local business and commuters and at worst puts them at risk of harm.”
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