While senior managers defended the process as independent, the union said only a promise of immunity would allow all employees to speak freely to investigator Janice Rubin.
There's no guarantee that your information or your identity is protected, said Carmel Smythe, president of the Canadian Media Guild.
"Every day, it looks less independent, that she's just now taking orders and supplying all the information to CBC."
CBC asked Rubin, a labour lawyer, to conduct an independent investigation after firing Ghomeshi, 47, as host of the radio show "Q" in October. The broadcaster said it axed Ghomeshi after seeing what it called "graphic evidence" he had caused physical injury to a woman.
More than a dozen other women then stepped forward with allegations he had physically or sexually attacked them, with one woman saying he had sexually harassed her at work but her complaints went nowhere.
Ghomeshi has denied the allegations, arguing that he engaged in "rough sex'', but insisting it was always consensual.
Earlier this week, the guild cautioned members that Rubin would be recording their interviews with her — information that could wind up being used in disciplinary proceedings against them.
CBC spokesman Chuck Thompson on Wednesday confirmed that could happen — but only after disciplinary proceedings had already started.
Essentially, he said, Rubin would flag the need to take action against an employee in her final report.
"If there's something that she believes needs to be brought to management's attention based on her investigation, she will do that," Thompson said.
"Any discipline that would be taken would fall to management."
Despite the guild's misgivings, one management source said those who had already spoken to Rubin were struck by her professional approach and had come away assured there would be no whitewash.
Among those who have spoken to Rubin was former "Q" producer Kathryn Borel, the woman who said she had complained to no effect about Ghomeshi to union representative Timothy Neesam.
Reached in California, Borel praised what she described as Rubin's rigorous fact-finding exercise but expressed doubt the investigation will ultimately yield much because people are afraid to speak out.
"How that information will be used, obviously, is where the process breaks down and where I stop believing that anything good will come from it, because management is far more interested in dodging and obfuscation than actually examining itself," Borel said.
"Fear and silence are what created this mess."
Just how tricky the situation is can be seen in an attempt by the guild to negotiate an agreement to protect Neesam's identity, which Rubin refused.
In a confidential letter obtained by The Canadian Press, Rubin spells out when a recording and transcript of her session with Neesam could be made available to management.
"Should the CBC request a copy of the material, it may also be given access to it by me but only if it engages in a disciplinary process with respect to Mr. Neesam in relation to the subject matter of the investigation," Rubin states.
She then goes on to state that "engages in a disciplinary process" means if and when Neesam first receives a notice to attend a disciplinary meeting.
Neesam has denied Borel mentioned sexual harassment to him, saying only that she talked about inappropriate behaviour.
Smythe said people want answers and a thorough investigation is needed, but Rubin's isn't the way to go.
"Many people want someone to be held accountable and actually so do we," Smythe said.
"We were very optimistic initially and each day we're a little less optimistic."
Ghomeshi is also facing sexual assault and choking charges stemming from alleged incidents involving three women. His lawyer has said he intends to plead not guilty.
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