The Scottish Court Service is owed £6.5 million in unpaid fines, according to figures.
A report on fines and financial penalties shows that £2 million worth of sheriff court fines remain outstanding for the financial year 2011/12.
The figure represents 13.4% of the total value of sheriff court fines due to be paid during the past year.
Fiscal direct penalties are £2 million in arrears for 2011/12 - representing 42.1% of the total value to be paid in the period.
Meanwhile, £1.4 million is still owed to Justice of the Courts and £1.1 million worth of antisocial behaviour penalties are also outstanding.
The Scottish Court Service said all outstanding fines and financial penalties are being pursued. Enforcement actions include benefit deductions, freezing bank accounts, arresting wages and seizing cars.
Commenting on the figures, Conservative justice spokesman David McLetchie said: "These levels of non-payment bring the whole system into disrepute and undermine public confidence in the justice system. We need to examine how we can more effectively collect such fines.
"Fiscal fines are supposed to be an alternative to prosecution, but when they are simply ignored by so many, the public will conclude that they are not much of an alternative."
Lewis Macdonald, Labour's justice spokesman, said: "It is completely unacceptable that one in three people are not bothering to pay a penny towards the fines imposed by our courts and this illustrates a major weakness in our justice system.
"The SNP Government has to address a situation where one of our courts' most common disposals has become unenforceable. Much of the £6.5 million in fine arrears is money lost to the public purse at a time when budgets are being squeezed."