The Scottish government has blocked two witnesses from giving evidence to the Alex Salmond inquiry.
The committee had wanted to question civil servants Judith Mackinnon and Gillian Russell next week.
But Deputy First Minister John Swinney refused the requests, saying it would create an "unacceptable risk" of complainers being identified.
Committee convener Linda Fabiani, an SNP MSP, said Mr Swinney's decision was "unacceptable".
Scottish Labour MSP Jackie Ballie described it as an "outrage", adding: "The secrecy and obfuscation of the Scottish government knows no bounds.
"The worst of this latest episode is that John Swinney is blaming the lack of written evidence for the non-appearance of these witnesses, when he is the one that is withholding the evidence. You really couldn't make it up."
And Scottish Conservative MSP Murdo Fraser claimed that the government was doing everything in its power to shut the inquiry down.
The committee is examining the Scottish government's botched handling of harassment complaints against Mr Salmond.
The government had to pay Mr Salmond £500,000 in legal expenses after admitting it had acted unlawfully because an investigating officer - Ms Mackinnon - had prior contact with one of the complainers.
Mr Salmond was cleared of 13 charges of sexual assault in March of this year after a trial at the High Court in Edinburgh.
The committee of MSPs set up to investigate the affair has consistently accused both the government and Mr Salmond of attempting to obstruct its work.
The government has not yet handed over legal advice that the committee has asked to see despite the Scottish Parliament voting for it to do so.
The committee had wanted Ms Mackinnon, who has previously given virtual evidence through an audio link to the committee, and Ms Russell - the Scottish government's workforce director - to give evidence next Tuesday.
But Mr Swinney refused the requests, claiming that it could "inadvertently breach either the undertaking or the court order preventing jigsaw identification of the complainers".
In a letter to the committee, he said he had "carefully considered the balance of those risks" and had concluded that "agreeing to these witnesses appearing on November 24 would create an unacceptable risk and therefore I cannot agree to the committee's request."
Mr Swinney said he would consider whether to allow the witnesses to appear in future if an agreement is reached with Mr Salmond's legal team.
And he said the government was still attempting to agree with Mr Salmond's lawyers what evidence can be released, and it could therefore not provide "uncontested documents, a timeline and a statement" about its handling of the complaints.
In reply, Ms Fabiani said it was unacceptable that the government was preventing the witnesses appearing because it "has not produced a timeline and statement to accompany documentation".
She added: "While the committee appreciates that no witness should be put in a position where they might inadvertently breach a court undertaking or court order, it is the Scottish government which has put its own employees in this position."