Essex CC's library service is owed more than £158,000 in outstanding fees and charges, according to council figures.
Customers are being urged to pay up and clear their debts, or face having their library service membership suspended.
A snapshot analysis reveals 43% of the debt is owed by just 7.3% of customers, 2,300 customers owe more than £15, £89,000 is owed in amounts ranging up to £15, and 79% of debtors owe less than £6.