The IFJ and MEAA today called on the Thai Government to immediately drop all charges against the pair.
The charges relate to the reproduction on phuketwan.com of a single paragraph from a Reuters special report on Rohingya boatpeople published in July 2013.
Reuters subsequently won a Pulitzer Prize for the investigation in 2014.
The journalists were charged with criminal defamation on April 17, 2014, under articles 326 and 328 of the Thai Criminal Code. The charges carry a maximum penalty of two years imprisonment and a fine of up to 200,000 baht (US$6000).
They were also charged with ; and violation of article 14(1) of the Computer Crimes Act, which carries a maximum penalty of five years imprisonment and a fine of up to 100,000 baht (US$3000).
Next week, on July 14, Morison and Sidasathian will face the Phuket Provincial Court. Following a three day trial, the judge is expected to consider a verdict for up to 30 days.
Since the military takeover of the country in May 2014, the IFJ has documented the a steady decline in press freedom with the ruling military junta in Thailand continues to repress and stifle the role of the media and freedom of expression in Thailand.
Alan Morison said: ''We are content to leave the decision to Thai justice, although some people have some concerns about the potential for a negative outcome. We feel committed to make a stance for a free media in Thailand.
This case was wrong from the very beginning, with one or two officers acting on bad advice.''
MEAA CEO Paul Murphy said: ''This is an outrageous assault on press freedom. It is an appalling misuse of the law with the intent of silencing legitimate journalism.
''The action by the Royal Thai Navy has been rightly condemned by the United Nations, the International Commission of Jurists and human rights and freedom of expression groups around the world.
''MEAA urges the Thai authorities to step back from the brink of making a dreadful decision and, instead, focus on the need for cooperation across the region to deal with the tragic plight of the Rohingya people.''
The IFJ said: ''The charges against Alan Morison and Chutima Sidasathian are a blatant attack intended to intimidate and silence Thailand's media - over the reprinting of an item of news that was a legitimate and now award-winning Reuters investigation into the Thai navy.
''This case must be condemned in the strongest possible terms and we strongly call for common sense to prevail and for all charges to be dropped.''
The IFJ represents more than 600,000 journalists in 134 countries
For further information contact IFJ Asia-Pacific on +61 2 9333 0946