Ian Blackford is being urged to break his silence after audio recording revealed he urged SNP colleagues to back sex pest MP Patrick Grady.
The SNP's Westminster leader has come under fire and opposition parties are calling for him to resign over the controversy.
Glasgow North MP Grady was found guilty following a probe which found that he had touched and stroked his victim’s hair, back and neck in a London pub in 2016.
The worker, who was 19 at the time of the incident, said earlier today that he is considering legal action over the case.
Last week SNP MP held a meeting to discuss the Grady case and at the gathering Blackford said: "He’s [Grady] going to face a number of challenges over the short term and so he should have our absolute full support.
"I for one very much look forward to welcoming Patrick back into the group next week. I am sure that everybody here will agree."
Now, John Lamont, Tory MP for Berwickshire, Roxburgh and Selkirk, is calling on Blackford to address the situation and resign from his post.
Lamont wrote to Blackford when the allegations were first published by the Daily Record last year. He has now resent his letter which asks a number of questions around support for the victim.
Lamont said: " Ian Blackford must break his silence and explain why he has taken no action to prevent sexual harassment in the SNP Westminster Group.
"Instead of acting as we requested more than a year ago, he has treated a disgraced MP with more sympathy than the victim who suffered harassment.
"But Ian Blackford has not only failed this victim, his disgusting actions have made it less likely that any future victims come forward.
"This horrible situation has been made even more ugly by the fact the SNP Westminster group is more focused on preventing leaks than preventing sexual harassment. Party discipline is more important to them than supporting a victim.
"The cover-up-and-close-ranks culture at the heart of the SNP Westminster group must end. That will only happen if Ian Blackford steps aside. He has betrayed a victim and that is unforgivable."
The SNP has also come under fire after its Chief Whip in the Commons Owen Thompson emailed all Nationalist MPs claiming that whoever made the audio relating to Patrick Grady has legal questions to answer.
Grady has been suspended from parliament for two day, while the SNP also withdrew the whip from the MP until he had served his suspension.
The Daily Record has contacted the SNP for comment.
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