Quebec's pension fund manager reported historic losses for 2008 this week in Montreal. (Canadian Press)

Opposition parties at the National Assembly are demanding the auditor general probe the record losses by the Caisse de Dépôt et Placement du Québec last year.

On Friday, a special legislative committee wrapped up 30 hours of hearings which heard testimony from past and current heads of the giant pension fund manager.

The Caisse saw the value of its assets plummet 25 per cent to about $120 billion from $155 billion last year.

According to the opposition, that's a far larger drop than that at other comparable pension boards, due largely to its large investment in asset-backed commercial paper. The Caisse took heavy losses when the ABCP market collapsed last year.

The Caisse purchased nearly $1 billion worth of ABCP after there were signs that the market was set to collapse, the opposition alleges.

The Parti Québécois, Action Démocratique du Québec , and Quebec Solidaire say the ABCP losses don't fully explain the poor performance, and they want an independent probe by the auditor general.

The leaders of the three parties signed a letter demanding Quebec Auditor General Renaud Lachance take a look into the Caisse's finances, but there will be no public inquiry unless the governing Liberals sign off on the proposal — something Premier Jean Charest has thus far refused to do.

With files from the Canadian Press