Flintshire Council faces a £585,000 bill to cover losses made by the Wirral and North Wales Purchasing Organisation.
Originally set up to save public cash, the organisation ran up debts of £1.2m before being taken over by a private company in 2003.
Denbighshire and Wirral Councils have battled for Flintshire to cover the bulk of the costs because it was the lead authority when the debts came to light. The other councils are expected to split the cost of £633,000 between them.