The leaders of the federal Conservative party and the Bloc Québécois both said Wednesday they cannot support the government's budget, setting the stage for a showdown vote next month in the House of Commons.

Finance Minister Ralph Goodale defended the $4.6 billion in changes to his February budget that were included in a deal Tuesday for the New Democratic Party to support the minority Liberal government.

"I would have preferred my original plan," Goodale told reporters in Saskatoon. "I would prefer not to have to make these changes."

Finance Minister Ralph Goodale

But it was clear his original budget would not have passed in the House, he said. "In a minority, you have to be flexible enough to make a minority work."

Opposition Leader Stephen Harper denounced the Liberal-NDP agreement as "death-bed conversions and deals with the devil."

"As soon as we get back, I will be asking our caucus to put this government out of its misery at the earliest possible opportunity," he told a business group in Amherstburg, Ont.

Opposition Leader Stephen Harper

The Commons returns to work on Monday, and the opposition must give 48 hours' notice of a non-confidence motion. That means a vote to defeat the government and force an election could come as early as next Wednesday.

The NDP pledged to support the government in any non-confidence votes until its budget receives royal assent, in return for a $4.6-billion increase in spending on social programs over the next two years.

"An NDP budget gives us no reason to support Liberal corruption," Harper told reporters earlier in Ridgetown, during a stop while he campaigned in southwestern Ontario. "This government is behaving in a completely irresponsible manner with the taxpayers' money. We're talking about a secret deal worth almost $5 billion to stay in power."

In Montreal, Bloc Leader Gilles Duceppe also said "we cannot support the government any longer."

He criticized the budget's proposal for controlling greenhouse gas emissions, to help implement the Kyoto Protocol.

"It's not a good budget for Quebec," Duceppe told reporters.

"We have proposed very concrete changes and they were defeated by the Conservatives and the Liberals. In this budget there is nothing with respect to the fiscal imbalance. There is nothing with respect to employment insurance, and there is nothing in terms of a good plan for Kyoto.

"There is more money for a bad plan, and this is not only what we are saying. This plan for the Kyoto Protocol is bad for Quebec."

Layton defends deal

Layton told high school students in London, Ont., that his deal with the government to increase social spending could cost the NDP politically, but his conscience demanded that he do the best thing for less fortunate people.

"I understand the criticism, and not everybody's going to like what we're doing," Layton said. "That's life, that's why we have a democracy. People will execute their judgment on voting day."

Answering questions from the students, Layton said, "I couldn't sleep at night if I knew that I had the chance to help some people get off the street and I didn't take it because I wanted the political advantage. I couldn't sleep at night."

Martin to court Conservatives over tax cuts

Meanwhile, Martin said Wednesday he will push ahead with tax cuts for big corporations despite his budget deal with the NDP, as long as the Conservatives support the move.

"We have pulled the large corporate tax cuts out of this budget to be pursued in a separate piece of legislation," Martin said in an interview with the Canadian Press in Ottawa.

"And that separate piece of legislation we'll introduce as soon as the Conservatives or somebody say they will support it. The corporate tax cuts remain intact. It's going to be up to the Conservatives to tell us whether or not they will support them."

The promise appears to fly in the face of the deal with Layton. Under that agreement, the Liberals said they would delay promised tax breaks for big companies, while keeping intact planned cuts for small- and medium-sized businesses.

"Mr. Martin has shown in the past year or so that he is capable of having any position at any time," Harper said on Wednesday. "And I think now, with the kind of corruption scandals this government is burdened with, he has shown he is going to do just about anything. And we can't allow a government to operate like this."