Figures published this morning show £37million of unpaid Council Tax went uncollected in 2011/12, while total Council tax arrears reached a new high of £84million.
Janet Finch-Saunders AM, Shadow Minister for Local Government, said, "It is grossly unfair that families in Wales are facing higher Council tax bills to subsidise the minority who refuse to pay their share.
"In challenging economic times, Councils should be working harder to collect unpaid taxes to limit increases in bills for hardworking and law-abiding taxpayers.
"While it may be unrealistic to expect councils to collect 100% Council Tax, total arrears now stand at a massive £84million – a significant sum, a fraction of which could freeze Council Tax for hard-pressed taxpayers.
"Having already been hit by Labour’s refusal to freeze Council Tax, Welsh households should not be unfairly penalised by uncollected taxes driving up bills even further.
"Considerable and persistent variation remains between local authorities, although I am proud that Conservative-led Councils were among the highest performing local authorities in delivering value for money.
"Welsh Ministers need to work constructively with local authorities to encourage sharing best practice so Councils can raise their collection rates and use the savings to reinvest in frontline services and reduce Council Tax bills for all."