Immigration Minister Jason Kenney continued to defend himself Monday against allegations he used official MP letterhead to solicit Conservative Party donations, as the opposition parties' calls for his resignation grew louder.

The letter in question, mistakenly sent to NDP MP Linda Duncan instead of its intended recipient Tory MP John Duncan, sought $200,000 in donations from various Conservative riding associations to fund an imminent advertising campaign targeting ethnic community voters.

It was also sent with briefing notes outlining the federal Conservative Party's plans for a $378,000 "pre-writ" campaign aimed at wooing ethnic voters before the end of March.

Kenney came under fire during question period in the House of Commons Monday. Deputy NDP Leader Thomas Mulcair and Bloc Quebecois Leader Gilles Duceppe both called on Kenney to step down, despite the minister's claims the letter was sent in error by an aide while he was rushing to attend a funeral abroad.

"When it comes time to cut ribbons there is the minister who is responsible, and he assumes his responsibilities and he looks good and he says, ‘I made that decision,'" Duceppe said in French. "But when the rules are broken it is no longer his fault, it's the assistant's…The ministerial responsibility applies all the time. He made a mistake, he's responsible, he should step down."

Mulcair accused Kenney of instructing his staff to use his MP letterhead, "which is of course completely illegal."

"His pathetic justification? He would normally be responsible but he wasn't physically present when the letter was written, therefore he's not. This passes the bounds of hypocrisy, even for a Conservative. He is responsible for these illegal actions, when will he resign?"

Kenney denied that he ordered his staffer to use his MP letterhead, brandishing papers in the House of Commons that he said were his personal stationary, which is supposed to be used for party correspondence.

"It ought to have been used in this instance, it wasn't, that was inappropriate, which is why the staff member in question resigned and I accepted his resignation," Kenney said.

Kenney also told the House that he informed both Speaker Peter Milliken and the ethics commissioner about the incident when he learned of the error.

"Obviously it was inappropriate, I apologize for the mistake that was made in my absence, and I believe that that is the end of it," he said.

Kenney said the incident had its roots in a conversation he had with some of his Alberta Conservative colleagues last Tuesday, during which he described an advertising plan to "trumpet" the work they have done on behalf of new Canadians.

Those colleagues asked for more information, Kenney said. The next day, as he was preparing to travel to Pakistan for the funeral of Shabaz Bhatti, the Christian Pakistani cabinet minister slain by gunmen on March 2, he asked an aide to send the information and specified that he should do so without using government resources.

The aide who sent the letter, Kasra Nejatian, had only been on the job six weeks. He resigned late on March 4, just hours after the letter came to light.

NDP MP Chris Charlton told Power Play that while personal letterhead may not be a government resource, staff are paid with taxpayer dollars, and therefore asking an aide to send such correspondence is still "not appropriate."

But Kenney said that while his aide failed to follow his office's protocol, it is not unreasonable for any staffer of any MP to "spend a couple of minutes trying to transmit information to caucus colleagues that was requested."

On Sunday, Kenney told CTV News he took responsibility for what amounts to a clerical mistake that went unnoticed because he was en route to Pakistan.

"Put it this way," Kenney said Sunday. "I was on a plane to Pakistan and if I had been in town it wouldn't have happened because I always insist on signing my own correspondence and if a mistake like that was made I would have corrected it."

But, amid accusations Kenney was wielding the influence of his ministerial office to raise funds for his Conservative party and opposition MPs calls for him to step down from cabinet, Kenney told CTV he has no intention of resigning.

As a 14-year parliamentary veteran, and one of Prime Minister Stephen Harper's most trusted political lieutenants, Kenney's political purview includes wooing votes from new Canadians living in regions key to pushing the Tories' minority government into majority territory.

Liberal MP Justin Trudeau said the incident blurs the lines by blending the role of the minister responsible for citizenship and immigration with the job of reaching out to "get as many ethnic votes as possible."

"The ethical concerns of blending what is a responsibility of a member of the executive of a country versus a partisan political operative to try and get as many votes as possible, is one of the things that is making Canadians more and more cynical," Trudeau told Power Play.

Kenney said the government has always been open about its effort to woo new Canadians by trumpeting Conservative values of low taxes, law and order and respect for family.

"Any party that wants to have a governing electoral coalition in the future is going to need to have a lot of support from new Canadians and members of our ethnic communities," he told Power Play. "We've made no bones about that."