Canadians avoided a fall election call last week, but Liberal Leader Michael Ignatieff says he doesn't know how much longer the Conservative-led government will survive.

"It's up to the prime minister to make this thing work, and to the other parties to make it work. I have no idea how long Parliament can survive," Ignatieff said Sunday on CTV's Question Period.

"I'm not going to sit there behaving unconstructively. But I'm saying very clearly: We do not have confidence in this government."

Last week, the Harper government managed to pass a ways-and-means budget motion in the House of Commons, which the NDP and the Bloc Quebecois supported. If the motion had been defeated, it could have sparked a fall election.

It marked the first time the NDP had supported the Tories since the last election. The New Democrats have said they will support the Conservatives at least until they pass proposed reforms to help unemployed workers. Those reforms could cost up to $1 billion.

In response, the Liberals offered to speed the passage of the EI bill so it can be approved before another confidence vote in October.

Polls have suggested that Canadians are reluctant to go back to the polls, but Ignatieff said his party can no longer prop up the government.

"I won't be one of those politicians who pretends that he doesn't look at polls," Ignatieff said. "Sure I look at polls, but this was a matter of principle for me."

"I've got a simple job, which is do I support this government or not," he added. "And I just came to the conclusion I just couldn't keep on doing it, and the (Liberal) party felt the same."

Ignatieff cited the growing federal deficit as one reason for his decision to try and bring about another election, saying the Conservatives have lost control of public finances.

He also pointed to Canada's relations with the U.S., which he said the Conservatives have let slip over the past four years.

"They didn't see the 'Buy American' stuff coming," Ignatieff said. "We have a very, very serious problem with this relationship, but I don't think I can fix it until I'm prime minister."

While other parts of the world are tearing down national barriers, such as the European Union, the Canada-U.S. border has been "thickening up," he said, making North America's economy less competitive.

"That's the line we have to get to Mr. Obama," Ignatieff said.