Scottish Labour leader Richard Leonard has called on the SNP to throw MP Margaret Ferrier out the party.
Ferrier, who represents Rutherglen and Hamilton West, confessed to taking a train journey from London to Scotland while knowing she had Covid-19.
She had already travelled south to attend Westminster despite having developed Covid symptoms and booked a test.
First Minister Nicola Sturgeon has called on the parliamentarian to resign, with the SNP withdrawing the party whip on Thursday evening.
But Leonard said said the “only step available” now was for the party to expel Ferrier.
He said on Monday: “Having had the weekend to reflect on her action, Margaret Ferrier has shown she is more interested in keeping her Westminster salary and perks than she is in doing the right thing.
“The only step available to the SNP leadership now is to expel her from the party.”
Scottish Conservative leader Douglas Ross said on Sunday he was “surprised, amazed and shocked” that Ferrier had not yet resigned.
Leonard and Ross are not the only politicians to call for Ferrier’s resignation thus far, with SNP MPs David Linden, Kirsty Blackman and Stephen Flynn also calling for her to quit.
Ian Blackford, the leader of the SNP at Westminster, told the Daily Telegraph Ferrier should resign in a bid to save her “self respect and dignity”.
‘She has to preserve her own self respect and dignity and do the honourable thing.’Ian Blackford, leader of SNP at Westminster
“Margaret has to respect the fact there’s been a breach of trust between her and the electorate,” he said.
“She has to preserve her own self respect and dignity and do the honourable thing.
“A failure to resign on her own terms means she will face a parliamentary standards inquiry.
“Nobody knows where that will go but she runs the risk of having her fate being taken out of her hands.”
In a statement last week, Ferrier said: “I apologise unreservedly for breaching Covid-19 restrictions by travelling this week when I shouldn’t have.
“There is no excuse for my actions.”
Ferrier and the SNP have been contacted for comment.