Unions are in a new battle with Brighton and Hove City Council after tens of thousands of pounds too much was paid to employees.
The mistake was made in the 2008 pay package agreed between union officials and the council but the error only came to light when a negotiated pay rise of around 2.75% was agreed in March of this year.
It is believed around 160 employees in various departments have been affected, each being overpaid up to £500.
The council wants to recover the money - totalling up to £80,000 - over the next few months.
But the Unison and GMB unions have warned they will fight any attempt to make the staff hand back the money - even though the workers were not entitled to it.
A council spokesperson said discussions would be held with the unions over how to reclaim the money.
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