Welsh Lib Dems would cut the basic rate of income tax to help "ordinary workers" once the power passes to Wales, its leader has said.
Kirsty Williams promised a costed plan to cut the 20% starting rate to 19%.
She said the Lib Dems had cut taxes for low and middle-income earners during the UK coalition government.
She denounced the Welsh Tories for promising to prioritise tax cuts for higher earners, and expected Labour and Plaid Cymru to defend the status quo.
During his Autumn Statement last Wednesday, Chancellor George Osborne said control of some of the income tax levied in Wales could be devolved without a referendum.
The sharing of tax powers between ministers in Cardiff and London would mean the Welsh government controlling £3bn of taxes a year by 2020.