Red-faced Birmingham City Council officials have admitted shooting themselves in the foot by over-estimating the number of employees suffering hefty wage cuts in the single status pay and grading review.
With angry unions planning their second one-day protest strike next week, the local authority said data depicting the number of losers under the new system had lumped part time and full time workers together - with the result that forecasts of some people losing as much as £30,000 a year were wildly inaccurate.
The estimates, produced by the human resources department and circulated to the media, failed to take proper account of thousands of staff - such as school dinner ladies and cleaners - who work only a few hours a week.
Instead, the figures were produced on a full-time-equivalent basis - showing how much part timers would lose if they worked on a full time basis.
The mistake handed unions a golden opportunity to criticise the council and agitate for strike action.
The original figures suggested 49 employees will lose between £20,000 and £30,000 a year.
The council now insists only six people will lose that much money.
An initial estimate that 741 people will be between £5,000 and £20,000 a year worse off was also wrong. The true figure is 523 people.
And no one will lose more than £30,000 a year, although it was originally said two people were in that category.
Cabinet equalities and human resources member Alan Rudge said the mistakes had harmed the council's case.
Coun Rudge (Con Sutton Vesey) added: "Some back room people just produced the figures which were not presented in a way that was easy to understand. It had a disproportionate impact and gave an incorrect picture of the effect on individuals.
"It looked far harsher than it really was." Just under half of the council union membership - 9,424 people - took part in the first one-day strike on February 5, according to payroll figures. If accurate, the figure means that just under a quarter of the 41,000 employees affected by the pay and grading review withdrew their labour.
Coun Rudge said he was hoping to hold talks with the unions before next Tuesday's planned stoppage.
He added: "As I have said, my door is always open.
"But I am still waiting for the unions to come back and address the issues we put to them. We have put loads of proposals forward to ameliorate the impact on individuals who stand to lose out.
"No one is getting a pay cut at all until April 2010 and I am trying to work to reduce the number of people who are affected to a minimum."
A three-year pay protection period, which means the new system does not kick in until April 2010, will reduce the number of staff facing wage cuts to fewer than seven per cent of the workforce, according to Coun Rudge.
He insisted the result of the pay and grading review, under which 48 per cent of employees will be better off, would be to end decades of salary inequalities between men and women and blue and white collar workers.
Coun Rudge added: "For the first time in the history of the council we are within the Equalities Commission's tolerance guidelines.
"I despair at some of the regional union officials who have been putting it about that what we are doing is enhancing inequality. It is nothing of the sort. We are actually addressing equalities issues that ought to have been dealt with decades ago."