The NDP is "incredibly focused" on holding Prime Minister Stephen Harper's Conservative government to account over the "plethora of scandals" surrounding it, the Official Opposition's new House leader said Monday as MPs returned to Parliament.

"The dynamic in Ottawa has changed. New Democrats are re-energized, reunited and ready," Nathan Cullen told reporters in the foyer of the House of Commons.

Cullen, who was appointed to his new role last week by NDP Leader Tom Mulcair, said the F-35s, potential electoral fraud, and Monday's revelation about an expensive hotel stay by International Co-operation Minister Bev Oda in London, are among the controversies associated with the government.

"As the scandals pile up, one of our challenges is which one to focus on," Cullen said.

Mulcair chose the federal budget cuts and their potential impact on services for Canadians as his line of attack in question period. He said the Conservatives are creating an "incredible economic, social and ecological debt." He also criticized the government over recently announced changes to the environmental assessment process.

Harper wasn't in question period to respond but Foreign Affairs Minister John Baird challenged Mulcair to explain budget cuts made when he was Quebec's environment minister and said Mulcair isn't respecting the joint responsibility between the federal and provincial governments on environmental assessments.

The Liberals, meanwhile, asked the government for assurance that a meeting on Tuesday of the public accounts committee on the F-35 fighter jet cost controversy wouldn't be held behind closed doors and that there wouldn't be restrictions on what witnesses are called.

Baird responded that committees are "masters of their own domains."

The committee held a meeting last Thursday and will meet again tomorrow to decide which witnesses to hear from in their study of the auditor general's findings on the F-35s. Michael Ferguson's audit determined that due diligence wasn't followed on the selection process for the F-35s and that the government's internal cost estimate was $10 billion higher than the one told to the public.

Liberals have accused the Conservatives of using their majority on the committee to stifle debate by holding sessions in camera and hearing only from Conservative-friendly witnesses.

Baird responded to further questions on the F-35s from the NDP and Liberals by saying the government will not "go to a garage sale to buy equipment for the men and women in uniform" and will follow the necessary steps to get them the best equipment.

The government was also questioned over its decision to close the Kingston Penitentiary and Leclerc Institution.

"All we know is that the NDP want prisoners out on the street. We want them safe and secure to protect Canadians," Public Safety Minister Vic Toews responded.

Monday was the first opportunity for the NDP to showcase MPs with new critic roles, following the announcement of Mulcair's new shadow cabinet late last week.

NDP loses MP from caucus

But Mulcair also had to deal with the surprise news a few minutes before question period that northern Ontario MP Bruce Hyer was quitting the caucus to sit as an Independent MP. Hyer said Mulcair's position that the NDP would bring back the long-gun registry if it wins government and being forced to vote a certain way along party lines were behind his decision.

He also mentioned the fact that he is not among the 77 MPs that were given a critic or deputy critic role by Mulcair motivated his decision.

Earlier in the day, Cullen said the NDP will continue to be "a party of proposition not just opposition," and that it is willing to work with the Conservatives and any other party to get something good done for Canadians.

Cullen also indicated what kind of approach he will personally use in his role as House leader, saying he won't allow the remaining weeks in the Parliamentary calendar before the summer break to be consumed by political antics.

"My goal is to ensure that even if our opponents are misbehaving and distracted in Parliament, our team remains steady and dignified," he said.

Tories expect tougher fight from NDP

Government House leader Peter Van Loan said on Sunday the government is prepared to defend itself and expects a tougher fight from the NDP with Mulcair's new team in place.

"I think that perhaps we'll all see a sharpened focus on policies and policy differences between us," Van Loan said.

While the NDP will begin to paint the government as fiscally irresponsible, the government is already at work painting a negative picture of both New Democrats and Liberals.

According to Van Loan, the Tories want Canadians to see the NDP as "a party that is committed to higher taxes, big government, larger debt and deficits, and preventing the job creation that we could see from responsible resources development."

The Conservatives have been running attack ads against interim Liberal leader Bob Rae since March.

Opposition MPs made it clear before MPs returned from their ridings on Monday that F-35s and budget cuts would be hot topics on Parliament Hill this week.

In an interview Sunday, Liberal House leader Marc Garneau called for the resignation of Defence Minister Peter MacKay, saying "there is a problem with military procurement, whether we are talking about the F-35s or armoured vehicles."

"If this government wants to show that it is accountable, then somebody has to pay for the mismanagement that has occurred. So far, all we have seen is cover-up.

"The minister of defence bears a major responsibility. It's not acceptable for him to say he was not properly informed about it. He should be fired," Garneau said.

The federal budget will also come under scrutiny as the government moves to table its budget implementation bill and opposition parties continue to highlight the impact of the cuts.

While the Conservatives have maintained the majority of the cuts will not impact services to Canadians, the NDP House leader said the impact of the cuts is "extensive and growing."

"Slowly and painfully, we're seeing what the full extent of the cuts are to services to Canadians," Cullen said, pointing to areas like food inspection.

According to Van Loan, the government is simply looking for "more efficient ways" of delivering the same services Canadians expect.

On Thursday, Kevin Page, the parliamentary budget officer, is scheduled to appear before the House finance committee, where he is expected to update members on his economic and fiscal projections and to compare them with the government's budget.

Page will also provide MPs with an analysis of the economic impact of the budget, as well as the fiscal impact of the government's decision to raise the age of eligibility for Old Age Security.

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