Brighton and Hove's council tax figures have been published in the civic newspaper before they have been agreed.
The details of the budget are in the March issue of City News but a council debate on the tax is not due until tomorrow.
Leading Labour councillor Jackie Lythell has apologised for the mistake.
The deputy leader of Brighton and Hove City Council said: "They should not have been published at this time."
Tory opposition leader Brian Oxley complained after reading the paper before the budget debate tomorrow night.
The Tories, Liberal Democrats and Greens are all putting forward alternative budgets to the meeting.
However, it is likely the Labour-controlled authority will agreed to the proposed budget, which includes a 10.9 per cent rise in council tax.
Coun Oxley said: "I think this is an outrageous insult to democracy in Brighton and Hove.
"What point is there in having the meeting on Thursday at all if this is how the council is to behave?
"It is a complete slap in the face for councillors and for their constituents. It shows the administration cares nothing for the due democratic process."
Coun Lythell said the text had to be prepared beforehand so the paper could meet its deadlines.
But she said it was wrong to put it out prematurely.
Many people will not receive their paper until after the meeting has taken place.
Coun Lythell said the paper was relying on what had already been approved by the main policy and resources committee last week.
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules hereComments are closed on this article