The leader of Glasgow City Council has been reported to the Standards Commissioner over a claim she attempted to "smear" a fellow councillor.
Frank McAveety, the head of the local authority's Labour group, has lodged a complaint against the SNP's Susan Aitken with the Commissioner for Ethical Standards, claiming she has broken the councillors' code of conduct.
The complaint relates to a report in The Sun newspaper that Ms Aitken posted a picture of Mr McAveety to a private Facebook group for SNP councillors.
It included the comment: "If anyone feels like getting these nice photos of Frank McAveety enjoying hospitality in the Rangers directors' box out there..."
Mr McAveety claims this was an attempt to "stir up a sectarian divide" but a SNP spokesman claimed the post was a "joke".
Former Glasgow City Council leader Mr McAveety's letter states: "In context, these comments came amid outrage over a decision to withdraw support for a fan zone at Ibrox Football Stadium, leading to claims of political interference in a quasi-judicial decision."
It continues: "The comments, as reported with the images, indicate that the leader of the council wished members of her group to circulate this image, in an apparent attempt to stir up a sectarian divide on this issue.
"These comments and this coordination fall very significantly short of the behaviour that should be expected of anyone in public life."
He claims they breach two sections of the code of conduct relating to respecting colleagues and treating them with courtesy, including on social media.
Mr McAveety said: "In response to legitimate criticism, Susan Aitken has sought to stir up a sectarian divide that our city is trying to consign to the past.
"That is flat-out unacceptable. The leader of the council should reflect on her behaviour and whether this is the standard that Glaswegians expect.
"I have asked the Standards Commissioner to investigate this behaviour because I do not believe that it is fitting for behaviour for an elected member."
A spokesman for the SNP's Glasgow group said: "Everyone understood Susan's post was a joke, as evidenced by the fact nobody did anything with it."