Online users and media activists have insisted that sharing and "liking" political messages on social networks should not be a crime.
Information and Communication Technology (ICT) Minister Anudith Nakornthap on Monday warned social media users to be wary of sharing and clicking "Like" on social media posts, since they could be deemed as damaging to the country's security.
He also said postings that are political in nature or meant to stir up public confusion might be in breach of the Internal Security Act and Computer Crime Act.
The Computer Crime Act stipulates that whoever uploads data that is deemed to violate national security on to a computer system could face punishment of five years in prison.
The Technological Crime Suppression Division said yesterday it would summon four people for questioning after they posted messages on the internet about a possible coup.
The police said the posting had no basis in fact and could cause public panic.
The four people are Thai PBS political and security editor Sermsuk Kasitpradit, red-shirt leader Dechathorn Teerapiriya, Warunee Khamduangsri and another person who uses the online name of Yo Onsine.
Sarinee Achavanuntakul, head of the Thai Netizen Network, said the warning against online users is a curb on freedom of expression. It also shows how oppressive the Computer Crime Act is.
"Sharing and liking online messages are not crimes. People just want to pass on and exchange data with one another. They won't know what kind of content would be deemed to cause public chaos," she said.
Ms Sarinee also urged the ICT minister to explain more clearly the definition of messages that could be considered in breach of national security and what could risk engendering public panic.
At present, the definition seems so broad it could limit people's freedoms, she said.
Time Chuastapanasiri, a researcher at the Academic Institute of Public Media, insisted that citizens must be allowed to publicise their political opinions.
Sharing and liking political messages should not be prohibited, he said, adding that the government is wrong to issue such a warning against normal social media behaviour.
"We have to understand that national security is different from the government's security," Mr Time said.
"People can express their opinion about politics as long as they do not harm other people's rights or reputation.
"If they spread information that is defamatory, they should face charges."
The activist insisted that sharing information about the possibility of a coup does not endanger national security or violate the computer crime law.
The issue of a possible coup is one that concerns the public interest, he said.
The ICT warning generated many negative responses from Facebook users.
One user posted that she was not a lie detector.
She said she is entitled to click "Like" on a posting even if she does not yet know if the message is correct or not.
Another user said Thais can no longer express their opinions.
The user wrote that personal comments or opinions do not destroy national security.
Another user wrote that the ICT's threat is like a gagging order, with the assumption that people who held different views were all wrong.
Gp Capt Anudith yesterday said he acknowledged that everyone has the right to freedom of opinion and expression.
But this does not extend to posting opinions that falsify facts and could lead to public confusion, panic and economic damage.
He said it was too early to say what penalty would be applied to wrongdoers.