Macmillan Cancer Relief is calling on chancellor Gordon Brown to use this month's Budget to remove a £1 million VAT bill incurred by the charity on new buildings.
Macmillan says it spends £5.2 million a year on building treatment centres, information and palliative care units, which are subsequently transferred to the NHS, which owns and runs them.
The irrecoverable VAT bill for 2002 on this programme is estimated to be close to £1 million.
The charity has been lobbying the Government since last June on the issue but, despite an assurance that Customs %26 Excise would consider the problem, no action has been taken.
A spokeswoman for Macmillan said that the Budget on 17 April is the obvious opportunity for the tax burden to be removed.
Around 150 MPs have signed an Early Day Motion supporting the charity's case and another 50 have written to ministers on the issue.