High-profile whistleblowers have joined forces for the first time in demanding that the United Nations change a global system they say deters its thousands of staffers from exposing crime, corruption and other wrongdoing.

In a letter sent to Secretary-General Ban Ki-moon on Wednesday, nine current and former U.N. workers say current policies offer "little to no measure of real or meaningful protection" from retaliation that can include firing, harassment and intimidation.

Miranda Brown, the chief of the east and southern Africa section of the U.N. human rights office, said that within days of being called to testify in a major investigation of another U.N. agency where she had worked and alleged wrongdoing, she was told that her contract would not be renewed.

When she complained, she was told she would be transferred from Geneva to Fiji instead.

"I believe this is a result of reporting wrongdoing," she told The Associated Press. She has asked for the transfer decision, issued last year, to be reversed.

The spokesman for Ban, Stephane Dujarric, did not immediately respond Thursday afternoon to a request for comment.

The new letter wants Ban to extend whistleblower protection to the nearly 130,000 U.N. peacekeepers around the world as well as contractors and others who might speak up about wrongdoing. It also wants an external way to handles claims of retaliation, plus the option of external arbitration.

The whistleblowers said they have had no response from the U.N. Secretariat. There was no immediate comment Thursday from Ban's spokesman or from a spokesman for the human rights office.

"They want the issue to go away. Our thing is that the problem is spreading," said another whistleblower, James Wasserstrom, who lost his U.N. job after alleging a $500 million kickback plot involving U.N. officials in Kosovo.

His case played a key role in new U.S. legislation last year that requires the U.S. secretary of state to certify that each U.N. agency receiving U.S. funding follows best practices for whistleblowers.

Wasserstrom and the other whistleblowers are now asking the State Department to be more careful in this year's review.

"Like wax fruit that looks nice but can't be eaten, the WIPO policy serves only as an ironic display of what it should be doing but isn't," another of the whistleblowers, James Pooley, wrote in a letter to Secretary of State John Kerry last month about the World Intellectual Property Organization, the U.N. agency in which Brown had reported wrongdoing.

The State Department certified it last year.

The U.N. on Thursday announced the creation of a "panel of external experts" to study how the U.N. administers justice. It includes former U.N. human rights chief Navi Pillay, who left the post last year. But Beatrice Edwards, the executive director of the Washington-based Government Accountability Project and a signee of the letter to Ban, said the review had been planned for some time.

"Frankly, we get tired of the policy reviews, because the problem is not with the policy. It's that it's not implemented, no political will at the top to protect whistleblowers," she said.

Last month, her organization warned in a letter to the U.N. Internal Justice Council about the possibility of bias against staffers, especially whistleblowers. Of the cases before the U.N. Appeals Tribunal in 2013, the letter said, 72 percent of appeals filed by staff members were rejected while 18 percent filed by the secretary-general were rejected.