Sheffield City Council gave trade union convenors a huge pay rise, in some cases nearly double that of their previous salary, to do the same work.
The council boosted 14 union convenors' salaries from between £17.8k and £26.5k to £29k and £33k.
For a librarian and a driver this meant jumping four pay grades, according to documents released by the council.
Buried in a report presented at a recent cabinet meeting the council stated: “Mitigations also need to be found for two other pressures - the full year impact of re-grading Trade Union Conveners to Grade 7 (£136k) but not reducing the number as agreed in the original proposal.”
Meaning all council employees who were being paid below £29k-a-year to carry out full-time union rep work had their salary raised. All those on or above that figure had their pay protected.
In the report the council forecast a £506k total overspend on human resources.
Councillor Shaffaq Mohammed, Liberal Democrats leader, said it was a “totally scandalous” use of taxpayers money.
He said: “The long standing council subsidies of trade union convenor has been a hugely controversial issue, particularly in recent times when the city council has cuts services to young people and the elderly within the city while continuing to allocate over £350,000 of council tax payers money to pay for the salaries of city council employees to carry out work solely for the trade unions.
“It is totally scandalous that the council tax payers of Sheffield are now faced to with a further bill totaling £136,000 because the Labour run city council has now decided to almost double the salary of some of the city council employees undertaking full time trade union work.”
The council defended their decision and said they upgraded wages to make pay and job descriptions more consistent.
Coun Olivia Blake, cabinet member for finance and deputy leader of the council, said they are working to bring the overspend back in line with the agreed budget for next year.
She said: "The purpose of this exercise was to standardise the pay and role description of trade union conveners employed by the council. We know that having conveners saves the council money and is the right thing for the organisation when going through the challenges we are currently facing.
"Trade union conveners were upgraded to band seven of the pay-scale in November 2017 as part of a job evaluation process that is standard council procedure.
"Historically, trade union conveners worked to different job descriptions and grades and so the job evaluation process was implemented to create a consistent job description.
"The new framework was created in agreement with the trade unions to ensure that SCC operates within statutory guidelines and that the trade unions are able to contribute to the development, maintenance and operation of effective industrial relations.
"By making this decision it was known that there would be an additional budget pressure of £97k. To deal with this pressure there was an agreement to a review of the amount of facility time allocated to the unions.
"This figure reported is worst case scenario and strategies to mitigate this within the next year are being implemented as are the arrangements which will ultimately bring facility time costs back with the agreed budget."
Sheffield Trades Union Council did not comment.