Anas Sarwar claimed yesterday that the SNP is "mired in scandal" following the arrest of ex-chief executive Peter Murrell.
On the campaign trail in Rutherglen and Hamilton West, the Scottish Labour leader said that the SNP was "known for their lack of transparency".
Murrell, who is married to former first minister Nicola Sturgeon, was arrested on Wednesday morning in connection with an investigation into the funding and finances of the SNP.
The couple's home in Glasgow was raided but 58-year-old Murrell was released after being questioned for nearly 12 hours.
Sarwar said: "The SNP is mired in scandal, mired in division, talking to themselves about themselves - and focused on their own priorities, not the people's priorities.
"Just like across the country, people in Rutherglen face the twin crises of an economic crisis and an NHS crisis. At this time they need an MP but they also need a government on their side."
Sarwar said there are "serious questions" for Sturgeon and First Minister Humza Yousaf over the investigation.
He added: "More broadly, on the Peter Murrell case, the SNP are known for their lack of transparency, their lack of accountability, that it's one standard for them and another standard for everyone else.
"The police have to do their job and complete their investigations. But there are serious questions for Nicola Sturgeon and Humza Yousaf about what they knew and when.
"I hope in the fullness of time we can get the appropriate answers."
Sarwar was in the constituency ahead of a potential by-election.
Former SNP MP Margaret Ferrier is likely to face a recall vote after the House of Commons' standards committee last week recommended she receives a 30-day suspension for breaking Covid rules.
She lost the SNP whip and received a criminal conviction after travelling from London to Glasgow by train while infected with coronavirus at the height of the pandemic.
At the time, Sturgeon said Ferrier should resign and Yousaf and the party's Westminster leader, Stephen Flynn, renewed the call last week.
However, Ferrier has not commented since the standards committee's recommendation was announced.
Sarwar said he could tell from being out on the streets that the public was not happy with Ferrier.
He said: "Rutherglen needs an MP that is on their side. Margaret Ferrier broke the law and risked people's lives at a time when people were making huge sacrifices across the country and weren't able to see their loved ones.
"At the same time she was risking people's lives by travelling on public transport while having tested positive for Covid. She was found guilty of that and an investigation in parliament found she should face a recall petition.
"When you're out and about in Rutherglen and Hamilton West, you can feel the anger, it's palpable, at how she has let them down, how she is mired in scandal."
Scottish Labour is still to select its candidate for the constituency, which it held between 2017 and 2019.
But the party is optimistic about its chances after a poll from earlier this week showed it had cut the SNP's lead to just five points.
The survey, from Redfield & Winton Strategies, suggested that the SNP would get 36 per cent of the vote at the next general election, while Labour was on 31 per cent.
This was a drop of three per cent from the previous month for the SNP and an increase of two per cent for Labour. It marked a huge change from the 2019 general election, where Labour won 19 per cent of the vote and sat in third place.
It also showed a significant drop for the SNP, who won 45 per cent of the vote in 2019.
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