OTTAWA - The war on terrorism has become the first test of Stephane Dion's fledgling leadership, laying bare ideological and ethnic rifts within the Liberal party.

The matter could come to a head as early as Wednesday, when MPs vote on a government motion seeking parliamentary approval to extend two provisions of the Anti-Terrorism Act, involving preventive arrests and special investigative hearings.

Dion said Tuesday that he expects Liberal MPs to unite behind his decision to oppose extension of controversial anti-terrorism measures.

And he said he won't change his mind, despite pressure from some of his MPs, former cabinet colleagues, Jewish groups and families of victims of the Air India terrorist bombing.

"The decision is final and we made a good decision for Canadians," Dion told reporters.

Dion refused to say what fate might await any Liberal MP who defies him and supports the motion.

"You know what is the rule. When we make a decision, we vote with discipline. Beyond that, it's a matter for internal discussion within the caucus," he said.

But in a taste of the high-pressure tactics that are already being brought to bear, the president of Liberal MP Roy Cullen's Toronto riding suggested Tuesday that the MP shouldn't be guaranteed the right to run for the party in the next election if he can't show loyalty to the leader now.

Cullen has been one of the most outspoken Liberals in supporting extension of the anti-terrorism measures. Indeed, he said last week that he was trying to recruit at least 30 other Liberals to defy Dion and ensure approval of the government motion.

But Ranjeet Chahal said the executive of Cullen's Etobicoke North riding association doesn't agree with the MP's stance.

"There's a line and if he doesn't agree with that, then he should open the nomination and let all the members of the riding decide," Chahal, riding president, said in an interview.

"In the end, we have to stand beside our party leader."

Cullen could not be reached for comment. However, other MPs did not immediately rally to Dion's call for a united front.

Toronto MP Derek Lee said he personally favours extending the anti-terrorism measures but hasn't yet decided how - or if - he'll vote.

"I tend to think that the (terrorist) conspiracy that gave rise to them is still out there," Lee said, noting that "I can't take my shampoo on an aircraft. We have to taper a lot of what we do now based on security concerns."

Montreal MP Irwin Cotler, a former justice minister and human rights advocate, also refused to say how he'll vote. But he reiterated his belief that the measures, brought in by the previous Liberal government in the wake of the Sept. 11, 2001 terrorist attacks on the United States, should be retained.

"We find that they have not been used and certainly have not been abused. But they might still be needed."

Dion has repeatedly said that Liberal caucus members were consulted before the decision was taken to oppose extension of the two provisions.

But MPs privately complain that the decision was taken by the caucus social justice committee, which is dominated by left-wing Liberals. Most MPs, including those with expertise in national security and human rights matters, were never consulted and were surprised when the decision was presented to them two weeks ago as a fait accompli.

Some privately grouse that Dion has been influenced by militant Sikh and Muslim groups, members of which helped secure his leadership victory last December.

Those complaints were echoed Tuesday by the chairman of the Air India Victims' Families Association.

"It looks like the sympathizers of terrorism have more influence on (Liberals)," Gupta said.

He said Dion may have become "victim of vote bank politics," referring to ethnic bloc voting.

The association fears that scrapping the provision on investigative hearings could hurt the ongoing investigation into the 1985 Air India bombing, Canada's worst act of terrorism which took the lives of 329 people.

The association is lobbying MPs to support the government motion, as is B'nai Brith Canada.

Frank Dimant, the Jewish organization's executive vice president, said he too has heard speculation that the Liberals are "pandering to certain specific groups within the Canadian society."

"In a way, it's a little bit of a continuation of what happened at the Liberal leadership convention. This seems to be becoming more of a pattern," he said.

While B'nai Brith is giving Dion the benefit of the doubt thus far, Dimant said the party will pay a price if the leader doesn't change his mind.

"This stench will go well beyond our community. National security impacts every Canadian in this country and I think Canadians simply cannot comprehend how it is that a party which brought in this legislation now turns on its own legislation."