Local authorities face paying billions in compensation to women workers in equal pay cases, a report suggests.
Cleaners have received compensation payments
Councils in north-east England have already paid about £100m while in Scotland pay-outs could reach £560m, reported Income Data Services (IDS).
Other councils had "larger workforces and therefore larger equal pay liabilities", the research group said.
IDS said pay-outs had been made to women denied access to bonuses that could add up to 80% to basic pay.
Sally Brett, of IDS, said: "Women working as school caterers or home helps are doing jobs of equal value to men, working in refuse collection, gardening or maintenance, and have been on the same pay grade as them for many years, but they have been denied access to the regular bonus payments that the men have received."
IDS said local authorities were struggling to implement new equality-proofed pay and grading structures without additional government funding similar to that given to other parts of the public sector like the NHS.
"Councils across Britain, many with larger workforces and therefore larger equal pay liabilities than the Scottish and north-east councils, have the same legacy issues to deal with," said Ms Brett.
The women's campaigns have been backed by the GMB and Unison unions in the past and IDS said no-win, no-fee lawyers were seeking to represent workers with "such transparent equal pay claims".
"We could soon see the bill for back pay compensation in local government reaching into the billions," said Ms Brett.