Funding row over devolving income tax powers
Attempts to tie increased funding for Wales to the devolution of income tax were blocked by Welsh Liberal Democrat leader Kirsty Williams.
She said it was "unreasonable" for the Conservatives to make top-ups to the Welsh government's budget conditional on a tax-varying powers referendum.
The Wales Act allows the Welsh government some control over income tax, subject to a referendum.
David Cameron has called on Labour in Wales to back the referendum.
Since the Act was introduced last year, the UK government has committed to a "funding floor" - something designed to protect the Welsh budget from being squeezed under the Barnett formula.
The floor will be introduced "with the expectation that the Welsh government will call a referendum on income tax powers", the UK government has said.
The prime minister last week urged the Welsh government to "get off the fence" and say Yes to a referendum.
However, speaking to the Western Mail he suggested the referendum and fair funding were linked, adding: "The funding floor and the referendum, those are the things that all go together."
Ms Williams told the BBC's Sunday Politics Wales her party believed in giving the Welsh government income tax-varying powers.
But added: "I do not think it is reasonable for the Tories to say you can only deal with Wales' under funding if you have that income tax referendum."