The letter, published by the American Association for the Advancement of Science, followed an incident in Australia earlier this month when university researchers were rushed to a secure location after receiving death threats.
"Scientists should not be subjected to fraud investigations or harassment simply for providing scientific results that are controversial," said the letter from the board of the AAAS, which publishes the journal Science.
"AAAS vigorously opposes attacks on researchers that question their personal and professional integrity or threaten their safety based on displeasure with their scientific conclusions."
A press release to journalists accompanying the board's letter mentioned that in Australia, "top climate scientists have been targeted by an unrelenting e-mail campaign that has resulted in police investigation of death threats."
US scientists have also been targeted by an activist group known as the American Tradition Institute which is seeking detailed records from climate researchers.
ATI "has asked the University of Virginia to turn over thousands of e-mails and documents written by Michael E. Mann, a former University of Virginia professor and a prominent climate scientist," the AAAS release said.
"ATI also has sued NASA to disclose records detailing climate scientist James Hansen's compliance with federal ethics and disclosure rules."
The AAAS letter noted that scientific progress depends on "full transparency" and data sharing, but said activist data requests are a "distraction and make no constructive contribution to the public discourse."
"The sharing of research data is vastly different from unreasonable, excessive Freedom of Information Act requests for personal information and voluminous data that are then used to harass and intimidate scientists," the board said.
The Australian National University said earlier this month that some of its scientists faced threats they would be attacked in the street if they didn't stop their research.
ANU vice-chancellor Ian Young said the menacing emails and phone calls had intensified in recent weeks amid heated public debate over Prime Minister Julia Gillard's plans to introduce a tax on carbon emissions aimed at reducing pollution.
In 2009, a major row over hacked emails from climate scientists erupted in Britain.
Skeptics claimed that emails from the University of East Anglia's climate research unit showed the scientists had manipulated and suppressed key data to support a theory of man-made global warming.
Two independent panel inquiries and a parliamentary probe subsequently cleared the scientists of any dishonesty or wrongdoing.