PQ leader Pauline Marois (Clement Allard/Canadian Press)

One day after Quebec's labour minister resigned from cabinet over his controversial stake in an asphalting firm, Parti Québécois Leader Pauline Marois says David Whissell should also step down as a member of the national assembly.

Under fire from opposition parties, Liberal Premier Jean Charest made an about-face Wednesday, announcing Whissell's resignation and confirming he was tightening ethics rules for cabinet ministers.

Whissell owns a 20 per cent interest in ABC Rive-Nord, a company that has won millions of dollars in government contracts. During Whissell's time in cabinet, the value of contracts obtained by the company doubled.

However, the MNA for Argenteuil said there was no conflict of interest because his shares were in a blind trust.

While Charest maintains there was never any favouritism, the premier now says ministers will no longer be able to hold any stake in companies that bid for public contracts.

But Marois says that doesn't go far enough. As a backbencher, Marois said, Whissell can still influence the government's key decisions.

She said the PQ will continue to press the issue this fall as a national assembly committee debates the Charest government's proposal to hire an ethics commissioner. So far, the government and opposition parties have failed to agree on how far-reaching the commissioner's powers should be.

Marois says the PQ will also demand the premier release details of his own income, and its sources. Last year, Charest acknowleged the Quebec Liberal Party has been supplementing his annual salary by $75,000 since 1998.

With files from The Canadian Press