Councillor Billy McAllister, colleague David Turner and other SNP councillors have refused to stand up for the Lord Provost at full council meetings for more than six years, putting it down to "long-held republican views".
As well as chairing full council meetings and representing the authority on civic and ceremonial occasions, the Lord Provost - currently Labour's Sadie Docherty - is ex-officio the Lord Lieutenant of Glasgow, and the Queen's representative in the city.
In a bid to quell the protest Glasgow's ruling Labour group sought expert opinion.
Now constitutional and local government law expert Jean McFadden, a former city council leader, has ruled the protest is without foundation. But the SNP accused Labour of using old pals to make up rules and said Labour had a personal vendetta against SNP deputy group leader Billy McAllister.
The snub was largely ignored from 2007 to 2012, but it has become an issue in the last two years.
Mrs McFadden, a former law lecturer, said the city council was formed under section 1 of the Local Government, Etc (Scotland) Act 1994.
She said: "The Lord Provost is not acting as a representative of the Queen when chairing a council meeting. When chairing council meetings, the Lord Provost does so as the convener of the council under section 4(1) of the 1994 Act … When acting as Lord Lieutenant, the Lord Provost acts under section 1 of the Lieutenancies Act 1997 and that does not apply during a meeting of the council."
Mrs McFadden said the mace used by the Council was presented to Glasgow Corporation in 1912 by the 5th Earl of Rosebery. He called it "a symbol of the honour, of the power and of the dignity of this noble and generous city".
She added: "To refuse to stand when the mace is brought in is a sign of disrespect and contempt, not only for the Lord Provost, but for the present City Council."
An SNP group spokesman called the ruling "cringeworthy and embarrassing" and added: "The Lord Provost has got her pal to rewrite history to justify the pomposity on display here. The Labour Party's personal dislike for Councillor McAllister has reached a new low."
Labour's Martin McElroy said respect for the chair is vital to meetings, adding: "I am sure that in the future this [standing] is something all councillors will do."