The implementation of the Milton Keynes roof tax is being delayed because of uncertainty over the government's proposed planning gain supplement.
Roger Humber, chairman of Milton Keynes Forward consortium of local developers, said it would not be pressing ahead with the tax until the Treasury promised not to impose the PGS.
Developers are concerned that they could be taxed twice - once when they pay the roof tax at the point for securing outline planning and again with the PGS if they go back for revised consents.
Humber said: "We want a statutory recognition that agreements like ours are ringfenced."
Under Milton Keynes' proposed roof tax, developers would pay a flat rate of £18,000 per unit to help fund the infrastructure required to support the area's development.