Nicola Sturgeon faces a series of questions over her meetings with Alex Salmond during a Scottish Government probe into sexual misconduct claims against him.
Labour has written to the First Minister demanding answers after she told MSPs she met Mr Salmond three times and spoke to him on the phone twice during the investigation.
Two women lodged formal complaints with the Scottish Government against the former first minister in January 2018.
Mr Salmond denies the allegations, and on Tuesday won his legal case contesting the way in which the complaints against him were handled, with a court ruling the Government had acted unlawfully.
In a statement to MSPs the same day, Ms Sturgeon said she met him twice at home, as well as once in Aberdeen before an SNP conference, and also spoke to him twice on the phone while investigations were ongoing.
She said Mr Salmond told her about the complaints and his concerns about the process.
Labour has now claimed the meetings “could have compromised the investigation”.
In the letter to Ms Sturgeon, the party’s equalities spokeswoman Pauline McNeill said: “These women, and the public, will have expected at the very least a competent investigation into these most serious of matters.
“They have been badly let down by your administration.
“In your statement to Parliament on Tuesday, you admitted to having spoken to Mr Salmond about the investigation your Government was conducting into him on five separate occasions last year.
“According to your statement, Mr Salmond used these private contacts with yourself to ‘set out his various concerns about the process’ and tell you ‘about proposals that he was making to the Scottish Government for mediation and arbitration’ regarding the investigation.”
Ms McNeill questions why the meetings were not listed in ministerial diaries, and Ms Sturgeon’s assertion they were “not Government meetings”.
The Labour MSP continues: “That is not credible. These were discussions between the current First Minister speaking with a former first minister about a Scottish Government investigation into alleged misconduct in office.
“Your decision to meet and hold phone calls with Mr Salmond on multiple occasions about the investigation could have compromised the investigation.”
She ends with a string of questions, including why Ms Sturgeon continued to meet with her predecessor after being made aware of the investigation, if any records were created, and if the full contents of the discussions will be released.
The SNP leader is also asked if she informed Permanent Secretary Leslie Evans post-discussion and if the senior civil servant offered any advice.
Further, Ms Sturgeon is questioned whether she sought advice on the potential of her contact with Mr Salmond to prejudice the investigation and if any members of her office or special advisers also contacted him during this period.
In her parliamentary statement, Ms Sturgeon said: “I was always clear that I had no role in the process and I did not seek to intervene in it at any stage – nor indeed did I feel under pressure to do so.”