The letters, from the organisation's Melbourne office, said there was "some danger that the NSW Parliament will blindly and foolishly follow the example of the Victorian Parliament taking some action against Scientology."
The letters told Scientologists that as voters they exerted more influence than they might think and they should approach their local Members of Parliament.
"If you want Scientology to stay and flourish in NSW, you can help bring this about by contacting your Member of Parliament or any other Member of Parliament with whom you wish to communicate," the letters said.
"To have such legislation passed would be a step in the direction of the Dark Ages and a degradation of the right to freedom of thought for which so many have fought for so long.
"Now is your time to strike a blow for the freedom of Man, to be among the valiant protectors of Man's most sacred right."
The letters were addressed "Dear Scientologist" and signed "Yours sincerely, L. Ron Hubbard."
A telephone switchgirl at the Sydney office of Scientology refused to relay a reporter's call today to a spokesman.
"We are not making any comment," she said. "No comment at all."
When the reporter told her he wanted to check details of the letter, she said, "No comment. It's for the eyes of those people alone."
The Victorian Government plans legislation to curb Scientology as a result of a report by a Government board of inquiry.