Thai Lawyers for Human Rights, which provides legal aid to those who fall foul of the junta, had been due to launch a report on the kingdom's faltering rights record at the Foreign Correspondent's Club of Thailand (FCCT) on Thursday evening.
But in a statement released today afternoon the FCCT said it had been forced to cancel the event "on the orders of the NCPO and the police".
The NCPO is the official name for Thailand's junta -- the National Council for the Restoration of Peace and Order.
The FCCT said the panel discussion was not sponsored by the club. Thai Lawyers for Human Rights had paid to use the venue.
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Club president Jonathan Head tweeted through his personal account that although the panel discussion was cancelled the club would remain open in the evening, adding that there would be "a visible police presence".
A junta spokesman, Major General Werachon Sukhondapatipak, confirmed the military halted the event, saying Thai Lawyers for Human Rights had not sought permission from the authorities.
Werachon said the junta had previously allowed political events to go ahead at the club if organisers contacted them in advance.
An attempt by Thai Lawyers for Human Rights to hold a similar event after the junta's first 100 days in power was also cancelled after junta pressure.
The organisation was not available for comment.
Thailand's generals took over in a May 2014 coup that toppled the democratically elected administration of Yingluck Shinawatra after months of sometimes violent street protests.