British Labour MEPs have been calling for all charges against Hall to be dropped immediately and for the Thai authorities to respect the rights of human rights defenders in Thailand.
Hall's trial is scheduled to go ahead in Bangkok on Thursday.
He is facing criminal defamation and computer crimes charges. It is over three years since an original criminal prosecution was filed against Hall.
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The trial is expected to continue until July.
This criminal case, with multiple charges filed, is the most serious of all the four cases brought by a Prachuap Khiri Khan province-based pineapple processing company - Natural Fruit Company - against Hall.
The charges were brought following publication of a Finnwatch report, 'Cheap Has a High Price', in January 2013. While this case was the first and most serious to be filed against Hall back in February 2013, it is the second case to actually reach a full criminal trial in Thailand's courts.
'Cheap Has a High Price' alleged labour rights violations at Natural Fruit's processing plant in southern Thailand, as reported from interviews with migrant workers from Myanmar. The interview data was analysed, assembled and a report was published by Finnwatch, whereas Andy Hall only coordinated the field research and, with a help of a team of others, conducted worker interviews for the report.
The criminal charges in this case carry a maximum combined penalty of seven years' imprisonment in addition to potential fines.
Hall was indicted on these charges in January 2016 when, pending trial and following granting of temporary release on bail, his passport was confiscated and permission to leave Thailand restricted without clearance from the court.
Hall said, “What I did was in the public interest for the benefit of migrants and that’s what I’ve been doing for 10 years. Conditions in the Thai seafood industry can be compared to modern-day slavery and that is something I was trying to highlight. I’m not going to back down because I’ve done nothing wrong.
“My work is not negative, it’s not bad, it’s not vicious, it’s intended to make things better. If they’re not willing to drop the cases, I am certain the pineapple industry, the Thai export industry and the Thai economy will suffer more.”
Hall has fought to protect human rights in south east Asia for the past 10 years and took part in key research which documented the dreadful treatment of migrant workers in a large Thai company.
With four separate charges, countless appeals, demands for false confessions and reports of witness intimidation Labour MEPs and the Trades Union Council (TUC) continue to call for his harassment to end.
Hall told this website, "I am confident that the criminal court system in Thailand will deliver justice in this case. Researching migrant worker conditions in global supply chains across Thailand is not and should not be a crime."
"This case is just another example of unacceptable judicial harassment of rights activists that remains far too prevalent in Thailand and across the region. Activists and researchers must be free to speak out in the face of serious rights violations without fear of prosecution or even imprisonment."
His case is backed by UK Socialist MEP, Glenis Willmott, who said, "I can't believe that Andy's trial has got this far. Andy has rightly highlighted the dreadful treatment of some migrant workers and the treatment that he has been subjected to by the Thai authorities is completing unacceptable.
"Labour MEPs have highlighted Andy's plight in European Parliament and to the Thai Ambassador. We have called on the Thai authorities to end this harassment immediately.
"Human rights are top of the EU agenda and we will continue to call for decent working rights for all workers across the globe."
Further comment came from TUC General Secretary, Frances O'Grady, who said, "The continuing prosecution of Andy Hall, without effective protest from the British government, makes a mockery of the British and Thai governments' claims to support human rights in global supply chains.
"This baseless judicial harassment of a human rights defender is continuing only to discourage others from standing up for justice in Thailand's exploitative workplaces. It should be stopped now, or it will leave a permanent stain on the reputation of Thailand's businesses."