NDP Leader Thomas Mulcair kicked off the first question period of 2015 by accusing the government of misleading Canadians on the mission in Iraq.

The opposition pressure comes after it was revealed that Canadian troops have engaged in at least three firefights with Islamic extremists in Iraq, leading to accusations of “mission creep,” or a change to the intended mission in the war-torn country. 

"We are proud of our forces. Less proud of a government that doesn't tell the truth to Canadians," said Mulcair. "Why did the government put them in harm's way after promising Canadians they wouldn't be at the front (lines)?"

Defence Minister Rob Nicholson maintained that the Canadian Forces are still doing exactly what they were sent to Iraq to do: "advise and assist" Iraqi troops.

"The Prime Minister says that if you shoot against Canadian Armed Forces, they will shoot back," Nicholson told the House.

The economy and plunging oil prices were also hot topics Monday. 

Oil prices have plunged to less than $50 a barrel, down from more than $100 a barrel in June, forcing the federal government to push back the budget to at least April. 

In question period Monday, Liberal Leader Justin Trudeau asked how much money the change in oil prices has cost the government. Finance Minister Joe Oliver said the government has made a $2.5-billion revenue adjustment to account for the change in prices. 

"What we're saying to Canadians is they should be reassured we have a strong economy and we will balance the budget and we'll honour our commitments,” said Oliver.

Speaking to CTV's Canada AM Monday morning, NDP finance critic Nathan Cullen said the Conservatives' economic plan is in trouble because they have invested so much in a single sector. 

"We don't really seem to have much of a plan B from the Conservatives. They've invested so much and put all of their eggs, in a sense, into the basket around oil,” said Cullen.

Liberal trade critic Chrystia Freeland said the Conservatives’ fiscal plan is in "tatters," accusing the government of spending their surplus on their long-promised income splitting plan. 

"In an absolutely reckless fiscal step, they spent the surplus, which doesn't exist, … on the Canadians who now need it least – on the top 15 per cent,” said Freeland. 

Income splitting would allow families with children under 18 to divide their incomes in order to reduce their taxes. 

Plummeting oil prices also forced the Bank of Canada to cut interest rates to 0.75 per cent last week, from 1 per cent. Freeland said the cut "is not the sign of an economy that is firing on all cylinders."

While the economy is expected to be front and centre this sitting, here are some other issues likely to dominate discussion on Parliament Hill:

  • National security: Prime Minister Stephen Harper revealed Sunday that the government will table its long-awaited anti-terror legislation this Friday. The legislation comes after a string of terror attacks around the world, including the ones in Ottawa and St-Jean-sur-Richelieu last fall. The bill is expected to give security agencies and police new powers. 
  • Canada's role in the ISIS mission: With Canada's commitment due to expire in April, the opposition parties will be pressing the government on what Canada's role could look like should it be extended. Canadians can expect the term "mission creep" to come up in the House a lot.
  • Federal election: Canadians are scheduled to head to the polls on Oct. 19 of this year. But rumours are swirling about whether Harper will drop the writ earlier. The Prime Minister has said he's not planning to call an early election.