The party's election manifesto said a funding floor would only be introduced after a referendum was called.
The St David's Day Agreement had said the vote would be an "expectation", and Labour Welsh ministers oppose a referendum before a funding deal.
Labour accused the Tories of trying to hold them "over a barrel".
The manifesto states the Conservatives would "introduce a 'funding floor' to protect Welsh relative funding and provide certainty for the Welsh Government to plan for the future, once it has called a referendum on Income Tax powers in the next Parliament".
But a Welsh Conservative spokeswoman told BBC Wales: "The St David's Day commitment we made to introduce a funding floor for Wales is firm and clear, and work is already underway at the Treasury and the Wales Office to bring this floor forward.
"The funding floor for Wales is not contingent on an income tax referendum. Our UK manifesto makes clear our expectation that the Welsh Assembly will hold a referendum on income tax raising powers early in the next Parliament.
"More detail of our ambitious plan for Wales will be announced in the Conservative Party Welsh Manifesto which will be launched later this week."
On Friday, Chancellor George Osborne told BBC Wales the funding floor would be between £113 and £116 per head for every £100 spent in England, the range recommended by economist Gerry Holtham. ​
Labour has said it would also introduce a floor to the Welsh government's funding, but has not committed to a figure.
Reacting to the Conservative manifesto, First Minister Carwyn Jones said:  "A vote for the Tories is a vote for a government that would cost Wales up to £300m a year.
"A fair funding settlement is either fair or it isn't - you can't impose conditions or try and hold the government over a barrel."
The Liberal Democrats have said they would commission an independent review of Wales' funding arrangements, with a view to raising the Welsh government's budget.
Plaid Cymru wants to see an extra £1.2bn a year given to the Welsh government, claiming it would bring spending into line with Scottish levels.
UKIP has said it would like to scrap the existing Barnett formula which determines funding for the four UK nations.
The Conservatives insist their policy on minimum funding for the Welsh government, subject to an income tax referendum, has not changed.