Montgomeryshire Senedd Member wants a referendum on the Council Tax rise set to his residents next month.
Newtown will have the third highest Council Tax in Powys after Welshpool and Machynlleth.
Russell George MS says residents should be able to have a referendum on the rise and any rise above five per cent in Wales.
In a statement he said: "Across Wales, Councils are currently sitting on over £2 billion in usable reserves, yet residents in Powys are facing a Council Tax rise of 8.9%. Year after year, the people of Wales are hit with Council Tax rises, with many having seen their bill double since 2010, yet Councils are hoarding billions of pounds in usable reserves."
He said the Welsh Conservatives have fought to keep council tax down across Wales by calling for an independent review of the Local Government Funding Formula and to ensure usable reserves are used to keep Council Tax low and introduce referendums for any council proposing a Council Tax rise above 5%.
He said: “Under the Welsh Labour Government, the Local Government Funding Formula remains broken.
“It cannot be right that people in Powys are facing such an increase in their Council Tax, whilst Councils across Wales are sitting on over £2 billion in usable reserves.
"As a party, we are committed to introducing referendums for any Council proposing a Council Tax rise above 5%. The Welsh Government should do the same, as it’s unfair on the people of Powys to have to suffer poorer services for higher council tax bills."
He added: “The Labour Welsh Government in the Senedd must do more to keep Council Tax as low as possible by encouraging the use of usable reserves, efficiency within the council and encouraging the sharing of resources across council boundaries, as well as correctly funding rural local authority areas."