A lawmaker has put forward a new proposal to limit the government's power to adjust levels of stamp duty. Martin Liao Cheung-kong of the commercial (second) sector, wants to build a rebate mechanism into the duty, imposed on companies buying flats. Under Liao's proposal, any changes to stamp duty levels announced by the financial secretary would have immediate effect, but they would also require Legco to pass a subsequent motion. Were the motion to fail, buyers would get a rebate from the government for extra tax paid. Liao calls his idea an example of a "postponed positive vetting mechanism". Under the current system of negative vetting, lawmakers scrutinise changes only after they come into effect. The government says this allows it to respond more swiftly to market changes than under positive vetting, where lawmakers scrutinise changes before they come into effect. "I support the cooling measures and I want to ensure speedy action in the light of the market's latest circumstances," Liao said yesterday. "But changes made to stamp duties should be subjected to Legislative Council approval." Housing minister Professor Anthony Cheung Bing-leung said the government would need time to study Liao's suggestion. Legco will debate the Stamp Duty (Amendment) Bill next week.