''We don't believe that people should go to prison for defamation, and laws that require that unacceptably violate human rights,'' HRW spokesman Phil Robertson told Phuketwan.
''What is particularly chilling about this case is the effect it could have to stifle independent research into right abuses and company supply chains in Thailand and the region,'' said Mr Robertson, the Bangkok-based Deputy Director of HRW's Asia Division.
Equally chilling is the absence of support for Mr Hall from the British Embassy or the British Government.
He is being treated with the kind of diplomatic disdain more appropriate for a person charged with sex offences against children.
British bureaucratic reserve is not appropriate in a case involving a respected rights campaigner with an international reputation, and clear-cut principles now being put at risk.
Mr Hall, 33, is facing civil and criminal action that could put him in jail for years and cost him 300 million baht in compensation.
Fresh accusations have now been made by Natural Fruit Ltd arising from the 2012 research by Mr Hall and a team from rights group Finnwatch, alleging violations of migrant labor rights at Natural Fruit's factory in Thailand.
The company has not directly responded to the specifics of the allegation but chosen instead, for reasons that have yet to be disclosed, to pursue Mr Hall individually through the Thai justice system.
British Ambassador Mark Kent told Mr Hall earlier this week via email that he intends to explain why the British Government is unable to offer him support in principle or in practice.
He has yet to do so.
Human Rights Watch has not shown the same hesitation. Spokesman Mr Robertson released the following statement yesterday:
"Human Rights Watch opposes criminal defamation, full-stop, anywhere we work around the world - and Thailand and the case of Andy Hall is no different.
''We don't believe that people should go to prison for defamation, and laws that require that unacceptably violate human rights.
''What is particularly chilling about this case is the effect it could have to stifle independent research into right abuses and company supply chains in Thailand and the region.
''And as a research organisation that looks into human rights violations, such a threat is unacceptable from our point of view.
''Obviously, getting the facts straight is critical but we've not seen any specific details from the company that substantiate what they allege was wrong about Andy Hall's report.
''Rather there seems to be a blanket accusation, which is worrisome. It's too bad that this whole matter is not being discussed directly between FinnWatch and the company, as was done by the other two companies named in the report.
''Human Rights Watch will continue to monitor this case very closely and take appropriate action as needed."
Mr Hall is now living and working in Burma. He visited Bangkok at the weekend and learned from Thai police of the fresh allegations involving two videos posted on the internet.
He now fears that, if Thai Government authorities decide to act on Natural Fruit's claims, he could be arrested when he makes his next visit.