December 1, 2008 at 2:02 PM EST

Liberal Leader Stéphane Dion will be prime minister of an unprecedented coalition government if Parliament defeats the Conservatives next week.

Liberal MPs announced the decision after a caucus meeting to review plans for the coalition, which reportedly include a pledge to pump billions of dollars into the economy

The three opposition leaders are drafting a letter to Governor-General Michaëlle Jean in which they formally call on her to allow the formation of a coalition government if the Conservatives are defeated on a confidence motion Dec. 8.

Opposition sources said Monday the drafting of the letter is at an advanced stage, and will be made public with the agreement of the leadership of the Liberal Party, the New Democratic Party and the Bloc Québécois.

The goal is to inform Ms. Jean that a viable alternative to the current government exists within the current Parliament, in the form of a coalition between the Liberal Party and the NDP. The Bloc is expected to promise to support the coalition to survive for at least a year, which would allow for the passage of two budgets.