More than 30 local councillors elected on a Labour ticket five years ago have split from the party, the SNP has claimed.
A survey conducted by the Nationalists found that almost one in ten of the 348 Labour councillors voted in in 2007 have either defected to other parties or sit as independents.
However, Labour disputed the list of 32 ex-Labour councillors as "riddled with errors" and a "spectacular own goal" in the run-up to the local authority elections.
The publication of the figures reflects the increasingly bitter nature of the contest between the two main parties in Scotland, particularly in Glasgow, where the SNP is hoping to deny Labour an outright majority at the election for the first time in 40 years.
Labour lost its working majority in March after several councillors resigned from the party. Many of them joined rebel group Glasgow First and will be standing against Labour candidates on May 3.
Labour's unrest began after 20 of its 46 councillors were told last year that they would not be standing for the party in the election.
SNP local government campaign director Derek Mackay said: "These figures are testament to a party that has seriously lost its way in local government and shows a breakdown in belief among many of its members.
"Labour's problems in Glasgow are well-documented but we see here that these fall-outs have been happening all across the country."
A Labour spokesman accused Mr MacKay of carrying out a "desperate, negative attack".
He said: "This spectacular own-goal is riddled with errors, including people who have never been Labour councillors or who have been actively deselected for not being good enough.
"If the SNP can't even draw up a list correctly, how do they think they can run a council?
"Being a Labour councillor is not a job for life, and those who don't perform get sacked.
"The SNP are so set on the referendum that they seem willing to tolerate inept, corrupt and offensive councillors in their party. We, by contrast, demand the highest standards because Labour puts you first."
Mr McKay has himself faced calls from Labour and the Liberal Democrats to step back from his role as local government minister until after the council elections next month.
Labour local government spokeswoman Sarah Boyack today echoed Scottish Liberal Democrat leader Willie Rennie's call for Mr MacKay should be "suspended" until May 3 following concerns about government announcements during the campaign.
Ms Boyack said: "Strict rules rightly exist to prevent ministers exploiting public office for party political gain and Derek MacKay has clearly overstepped the mark."
More About Local elections 2012
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- SNP fury as Labour and Tories strike coalition deal to run Stirling Council
- Voters go to the polls a week late to elect final three councillors
- Councils in Lothians strike deals after days of negotiations
- Councils across Scotland starting to take shape after days of negotiations
- Negotiations across the Lothians in the wake of local government elections