BANGKOK (AP) — Media reports in Thailand say authorities have declared it illegal to exchange information on the internet with three prominent government critics who often write about the country's monarchy.

A letter from the Ministry of Digital Economy and Society reported online Wednesday by the newspaper Thai Rath and other media advised all citizens not to follow, contact, share or engage in any other activity that would result in sharing information from historian Somsak Jeamteerasakul, academic Pavin Chachavalpongpun and online journalist Andrew MacGregor Marshall. All three live outside Thailand.

The letter says people who spread such information, directly or indirectly, could be violating the country's Computer Crime Act, even unintentionally.

Somsak has written extensively and in great detail about the Thai monarchy, and his detailed Facebook postings are often consulted even by royalists who disagree with his views. Pavin is an outspoken former Thai diplomat, and Marshall is the author of "A Kingdom in Crisis," a 2014 book.

Thailand enforces a law that punishes with three to 15 years imprisonment the dissemination of information considered insulting to the monarchy. Prosecutions have surged in the past decade as political turmoil coincided with the decline in health of King Bhumibol Adulyadej, who died last October.

Most cases of insulting the monarchy — lese majeste — are apparently based on information posted on the internet, and often are accompanied by charges under the Computer Crime Act, which was originally enacted in 2007. It is not clear what if any aspect of the Computer Crime Act applies in the case of Wednesday's order.

Thai authorities try to take pre-emptive actions against material it considers illegal, having local internet service providers block access and reaching agreement with some online services such as YouTube to bar access in Thailand to material.

In February, a student pro-democracy activist who shared a story about Thailand's new king that had been posted online by the Thai-language service of the BBC was indicted on a lese majeste charge. Jatupat "Pai" Boonpattararaksa pleaded innocent.

The BBC story included mentions about the personal life of King Vajairalongkorn Bodindradebayavarangkun — who succeeded his late father last year —and other material considered too sensitive to be publicly discussed in Thailand.

Thai authorities had previously warned that even Facebook "shares" — links to a posting, rather than the content itself — could be considered a violation of the lese majeste law. Jatupat had also posted several passages from the BBC Thai story.

Many human rights organizations inside and outside Thailand have urged its government to halt the use of laws that make it illegal to criticize the monarchy, calling them a political tool to stifle critical speech.