Parished areas of Northampton are being hit with a covert tax - an opposition group has warned - which could be earning the borough council up to £100,000 a year.
The Liberal Democrat Group on the borough council is calling for a rethink of the council tax increase imposed on residents in parish council areas.
The authority agreed to the increases at the end of February and tax demands dropped on residents' mats in March advising people of the increased charges taking effect from April 1.
Government law permits district and borough councils to raise tax by £5 on a Band D bill each year - and the equivalent amount on each of the other bands, which in Northampton's case is 2.4 per cent.
But the Lib Dem group is set to question a "special expenses charge" that has been applied to areas with a parish council, including Billing, Colingtree and Duston, which appears to have taken some payers' bill up by up to four per cent.
The Lib Dems believe this level of increase should have been put to a referendum and could gain the borough council up to £100,000 in additional taxes in the 2017/18 year.
Councillor Sally Beardsworth (Lib Dem, Kingsthorpe) said: "To fill the black hole in the Borough finances as a result of £10.5 million lent to the Cobblers the Conservative administration has imposed the maximum increase of £5, above which they would need to hold a referendum.
"The parished areas make up a third of the council tax payers and these residents have been charged an increase that is not allowed without a referendum.
"The Liberal Democrats call for a re-think to be discussed at the council meeting on the 24th April."
Councillor Brandon Eldred (Con, East Hunsbury), who is the cabinet member for finance, claims the Lib Dems are "mistaken".
“The legislation relevant to the setting of council tax rates is defined by central Government," he said. "We have strictly adhered to these principles and no-one in the borough of Northampton is paying a larger council tax increase than is allowed without a referendum.
“We have written to the person who raised this issue and explained that they are mistaken.”
The Lib Dems, however, intend to pursue the matter and have put forward a motion to the full council meeting on Monday, April 24, to see the special charges reconsidered.
Labour's shadow finance member Councillor Clement Chunga, (Lab, Brookside) said: "I have some sympathy with what the Liberal Democrats are saying on this occasion.
"Back in 2012 the Tory borough council looked to set up more parish councils in the town.
"Labour opposed this as it would mean residents paying an additional precept for things, the borough council should be doing anyway."