While the worst of the economic downturn is thought to be over, several building companies are on the brink of financial ruin, unionists says.

The Construction Forestry Mining and Energy Union says hundreds of workers could lose their jobs as a result.

The union's insolvency adviser Mark Franklin told AAP that subcontractors were owed about $8 million following the appointment of administrators to family-owned Sydney-based builder Whitehorse Constructions Pty Ltd last week.

"Hundreds of workers stand to lose their jobs and entitlements as Christmas approaches," CFMEU state secretary Andrew Ferguson said in a statement on Thursday.

"Despite recent reports that the worst of the economic downturn is passed, another 10 builders are teetering on the edge of collapse."