Under National Assembly rules, budgets cannot be amended. Speaker Jean-Pierre Saintonge made this decision in June, 1993, at a time when nobody envisaged a minority government. The PQ has asked that the rule be changed. Speaker Michel Bissonnet will likely announce his decision today.
If you take the opposition parties at their word, Charest will have to back off his taxcuts or face an election. Given the fact that Quebecers have already rejected Charest's election promise as a cynical attempt to essentially buy votes, it would seem political suicide to fight another election with these taxcuts as the centerpiece.
The Liberals may have gambled that the PQ wouldn't relish another election, as they re-tool. The stubborn budget may prove to be the final nail in Charest's coffin. While there is an argument for blaming the opposition for the cost of another election, Charest will still be forced to defend, allowing the other parties to argue substance over political expediency.