The Foreign Correspondents Club of Thailand was ordered to cancel its discussion on "Memories of 1932: The Mystery of Thailand's Missing Plaque" scheduled to be held at 7pm on Wednesday in Bangkok.
"The decision was made after the FCCT received a letter from police at the Lumpini station asking for the event to be called off," the statement read.
It quoted the police as saying they had been contacted by "relevant officials".
"In the letter, the police said the officials believed that the event posed a threat to national security and that it could be used by unscrupulous individuals to stir up disorder.
"The FCCT disagrees with this assessment. Our events are always well-moderated and allow for constructive and civilised discussions. This particular event was on a topic of great historic and contemporary relevance, with a panel of distinguished speakers," the club stated.
"However the FCCT has been given to understand that this cancellation is on the orders of the NCPO and we have no choice but to comply," it stated, referring to the National Council for Peace and Order.
Instead, the FCCT said it would mark the World Press Freedom Day on Wednesday with a discussion on the state of media freedom in Thailand.
Complaints were filed last month about the disappearance of the 1932 Siamese Revolution brass plaque that had been fitted at the Royal Plaza in Bangkok. The disappearance remained a mystery as concerned parties learned that local surveillance cameras were removed then.
The brass plaque marked the spot where the Khana Ratsadon group announced its revolution in 1932. The group of military and civil officers staged a bloodless coup against King Rama VII to change the form of government from absolute monarchy to constitutional monarchy.
The memorial plaque bore an inscription reading: "Here at dawn on June 24, 1932, Khana Ratsadon brings into being the constitution for the sake of the country's prosperity".
A new plaque replaced it with another inscription reading: "The respect for Phra Ratanattraya (The Three Jewels -- Buddha, Dhamma, Sangha), the state, one's family, and the faithfulness towards one's king will all contribute to the prosperity of one's state."