Greg Mulholland, member for Leeds North West, said organisations were drawing up plans for housing estates on protected sites and selling them on at 'grossly inflated' prices.
According to the MP, detailed development plans are often drawn up for plots of land - despite there being no planning permission secured - leading speculators to believe that a housing development will go ahead there in the foreseeable future.
But when the truth is discovered, the MP said investors put pressure on local authorities to change the land use.
The politician said: 'Unwitting investors, looking for a safe home for their money, can be duped into paying over the odds for land that needs to be protected, not built on.
'Then, when they've got tens of thousands of pounds tied up, they realise there's no plan for homes.
'Their only chance to get their money back is to get permission for development - and councils could then be put under undue and unethical pressure to review the status of the land.
'The green belts that protect out cities from urban sprawl are already under enormous pressure. Land banking could cost us some of our most precious green fields.
Buyers need to be warned about this unscrupulous behaviour as it could cost them dear.'