Councils are being forced to publish the cost of staff working on trade union duties, as part of an ongoing government transparency drive.
Announcing the new rules, communities secretary Eric Pickles said taxpayers 'had a right' to know how much council funding 'is being spent on subsidising council workers to act as union officials rather than working on frontline services'.
However Unison's head of local government Heather Wakefield emphasised trade union reps were not funded for their work and only received facility time to engage in industrial relations issues. Research from the Trades Union Congress (TUC) earlier this year suggested 16% of union reps say less than a quarter of the time they spend on union work was paid for by their employer.
Local authorities will now be required to make available information on how many employees are union representatives and the number that spend at least half their time on their duties.
Town halls have been told to make public their estimated spending on unions by calculating the number of full time days spent by employees on union duties against salary costs.
Local authorities will have until 2 February 2015 to publish annual information, which will be required every 12 months.
The new code will also require publication of council actions on fraud, household rubbish collections and spending of parking fines.
Pickles added: 'Greater power for local government must go hand in hand with greater local transparency and local accountability. Therefore it is only right we give council tax payers the data they need to play a bigger role in local democracy.'
TUC figures suggest every £1 spent on union facility time in the public sector creates a return of between £3 and £9 in accrued benefits, including savings on employment tribunals and staff recruitment.
Wakefield said: 'HR staff are dependent on Unison for training reps and ensuring they have expertise in such things as job evaluation and health and safety. Without trade unions, councils would not have been able to deliver equal pay reviews.
'Four years of vicious Government cuts to local councils and up to 500,000 redundancies have seen union reps acting as go-betweens between councils and employees. Many councils have testified to us that they couldn't have dealt with the cuts without their union reps.'