The WA Liberal party will vote against the state government's new tax on foreign buyers of residential property.

Shadow Treasurer Dean Nalder said the 7 per cent surcharge would add to the tax burden on the property market and weigh down house prices.

But the government insisted the tax, which would not apply to big developers or commercial property investors, would have a minimal impact on the local market.

"A record number of WA homeowners currently have negative equity in their homes and the McGowan Government wants to impose a tax that has been proven in the Eastern States to put the brakes on the housing market and force housing prices down," Mr Nalder said.