Finance Minister Victor Dominello has vowed to review how a Sydney home owner was offered less than an official valuation by the NSW Valuer-General for his property, forcibly acquired for the $16.8 billion WestConnex motorway.

Two days before a conciliation hearing in the Land and Environment Court on Tuesday over compensation he will receive, former St Peters resident Richard Capuano received a letter on behalf of the acquiring agency, Roads and Maritime Services.

The letter from law firm Clayton Utz revealed RMS was arguing the market value of his former home is $75,000 less than the NSW Valuer-General's assessment.

The Valuer-General assessed the market value of the St Peters terrace at $900,000 but RMS now says the value is $825,000. Mr Capuano's position is the market value is $1.675 million.