Stephen Harper is facing pressure to recall MPs to debate potential military intervention in Syria.
Mr. Harper had planned to prorogue Parliament and delay the return of MPs scheduled for Sept. 16 until mid-October, but opposition leaders are pressing the Prime Minister to consult the House of Commons before Canada takes on a mission in Syria.
Signals are increasing that the United States and Western allies will strike.
British Prime Minister David Cameron announced on Tuesday that he will reconvene Parliament early, on Thursday, to debate and vote on a response.
But Mr. Harper's spokesman, Carl Vallée, said the Prime Minister has no plans to follow suit. "It is premature to discuss recalling Parliament at this time," he said.
On a day when U.S. Defence Secretary Chuck Hagel said his country's forces are "ready to go," Mr. Harper provided his support in a phone call with President Barack Obama, agreeing that the world must respond to the use of chemical weapons in Syria in a "firm" and "timely" manner.
The regime of Syrian President Bashar al-Assad denies gassing its citizens, and Russia and China, veto-holding members of the United Nations Security Council, oppose military action.
But the United States and major allies, notably Britain and France, favour using military force to punish the regime, and several major news agencies report that Syrian rebel sources say Western powers told them at a meeting in Istanbul an attack could come within days.
Now opposition leaders in Canada are warning that Mr. Harper has an obligation to convene the Commons before he commits Canada to a role in a military action.
"If it has to go any further, Parliament should be consulted. There's no question about it," NDP Leader Thomas Mulcair said. "That's an obligation Stephen Harper would have."
Liberal Leader Justin Trudeau told reporters in Charlottetown that Parliament should be recalled now, and that Canadians need to be clearly informed by government "about what we are going to get involved in."
Foreign Affairs Minister John Baird briefed the opposition leaders on Syria in separate phone calls Tuesday. A spokesman for Mr. Mulcair, George Smith, said the NDP leader stressed in that call that "Parliament would have to be recalled if there was any direct military involvement," as well as the importance of "working with the UN."
Legally, Mr. Harper can deploy the military without asking for Parliament's approval, but he has previously sought a vote in the Commons when sending the Canadian Forces into action. He did so before extending the mission in Afghanistan in 2006 and 2008, and soon after he announced fighter jets would go to Libya in 2011.
Mr. Harper has not spoken publicly about what role Canada might play in Syria, but signalled his support for military action in a call with Mr. Obama on Tuesday morning.
"The Prime Minister made it clear that he shares the view that the recent chemical weapons attack was carried out by the Syrian regime and described the use of these weapons as an outrage," Mr. Harper's office said in a summary of the call. "Both leaders agreed that significant use of chemical weapons merits a firm response from the international community in an effective and timely manner."
Mr. Harper's government has been reluctant to endorse Syria's opposition coalition, let alone finance or arm it, because it has viewed them as divided, too sectarian, and tainted by Islamist extremists.
Mr. Harper's willingness to support action against the al-Assad regime may be in part because the United States and Britain insist their goal is not to force Mr. al-Assad from power.
International support would help build legitimacy for a military action that the UN Security Council will not endorse, given the opposition from Russia and China. Canadian backing could be part of that.
But Canada might take only a symbolic military role, especially if the action is a short burst of air raids or missile strikes.
The Canadian Forces have no planes in the region, and only one warship, the frigate HMCS Toronto, is nearby, on counterterror operations in the Arabian Sea.
This means Canada would not have time to take a combat role in a short air campaign, retired major-general Lewis Mackenzie said.
The Chief of the Defence Staff, General Tom Lawson, was in Jordan this week for three days of meetings on Syria and regional security with representatives of 10 countries, including the chairman of the U.S. Joint Chiefs of Staff, General Martin Dempsey, and military leaders from the region. A spokeswoman for the Canadian Department of National Defence, Jennifer Eckersley, said the meetings were planned months in advance.