Second home owners in Wales face a massive tax hike next year as part of a bid to curb soaring property prices and empty houses.
Councils will be able to set a second home and long-term empty premium of up to 300% from next April - potentially four times higher than what some people currently pay.
The maximum premium is 100% at present, meaning the new policy constitutes a possible tax rise of 200%.
Some local authorities may choose to apply different rates for second homes and long-term empty dwellings.
Councils are being encouraged to spend the extra cash raised on boosting affordable housing supply to make it easier for people to buy houses where they grew up.
But it comes as families face a cost of living crisis, with soaring energy bills and national insurance hikes from next month.
Welsh climate change minister Julie James said: "We want people to be able to live and work in their local communities, but we know rising house prices are putting them out of reach of many people, exacerbated by the cost-of-living crisis we are facing.
"There is no easy answer or quick-fix solution. This is a complex problem that requires a wide range of actions.
"We continue to carefully consider further measures that could be introduced, and these changes are the latest steps we are taking to increase the availability of homes and ensure a fair contribution is made."
Finance minister Rebecca Evans added: "These changes will give more flexibility to local authorities and provide more support to local communities in addressing the negative impacts that second homes and long-term empty properties can have.
"They are some of the levers we have available to us as we seek to create a fairer system."
But critics warned that families would be clobbered by the rise.
"It's astounding and morally indefensible," Jonathan Martin, a spokesman for the Home Owners of Wales Group, told BBC Radio Wales Breakfast.
"Where do they think we're going to get this 300% from? I can't afford it, that's for sure and I'm quite sure a lot of other people can't afford it. It's just astounding."
However the threshold for when owners pay business rates on self-catered accommodation will increase.
At the moment, properties that are available to let for at least 140 days and that are actually let for at least 70 days will pay rates rather than council tax .
But from next April, the threshold will increase for properties available to let for at least 252 days and actually let for at least 182 days in any 12-month period.
The ministers said the change is intended to provide a clearer demonstration that the properties concerned are being let regularly as part of genuine holiday accommodation businesses that are making a substantial contribution to the local economy.
