But the newly minted Liberal leader is hitting back, accusing the Tories of using the public purse to spread distortions and lies.
NDP Leader Tom Mulcair, meanwhile, says both the Conservatives and Liberals are equally guilty of abusing public funds for purely partisan purposes, although New Democrats have been known to do the same in the past.
Fierce debate about mass mailings by MPs erupted Thursday over news that Tory MPs are being urged to blanket their ridings with flyers bashing Trudeau as an inexperienced lightweight.
Harper told a news conference the campaign is well within the rules of the House of Commons, and MPs from all parties send partisan missives, known as 10 percenters, to their constituents.
"There are House of Commons rules for communications that we do with constituents across the country," Harper said.
"All parties work within those rules, and all parties use those activities and use those rules."
However, not all Conservative MPs are comfortable with the flyers, templates of which have been prepared for their use by the Conservative caucus research group.
"I won't be participating in that program," said Edmonton MP Brent Rathgeber, adding that his constituents "are not all that thrilled by negative attacks."
"I always, just myself, try to focus on policy rather than personality," said Kitchener MP Stephen Woodworth.
"I know there are other approaches and I can't tell other people what to do. But for me, it's different, it's a different way."
Various scripts prepared for the flyers argue that Trudeau has neither the judgment nor the experience to govern the country, and use partial or out-of-context quotes to make the case that he's "in way over his head."
That's the same theme the Conservatives are using to hammer Trudeau in television ads running across the country.
On a campaign stop for next month's byelection in Labrador, Trudeau said the Conservative government has become a one-trick attack machine.
"Instead of defending an increasingly indefensible, mediocre record on the economy and on various decisions, they attack and they use whatever public resources they can to turn people away from politics and to foster cynicism," he said in Happy Valley-Goose Bay.
"Whether it's a surplus of economic action plan ads on the taxpayers' dime or these 10-per-centers that do nothing other than distort, tell lies and attack, for me, that's something that Canadians are sick and tired of," Trudeau added.
However, Mulcair called Liberal complaints about the flyers "utmost hypocrisy."
He noted that Bob Rae, interim Liberal leader until Trudeau's coronation last week, recently sent out two partisan missives to voters in NDP-held ridings. And he accused Rae of using "subterfuge" to get around a ban imposed a couple of years ago on MPs sending 10 percenters outside their own ridings.
Rae sent his missives in "franked" envelopes, using MPs' unlimited right to send and receive postage-free mail anywhere in Canada.
The Liberals "howled the loudest" about out-of-riding partisan flyers two years ago, Mulcair said and yet, "Bob Rae was using exactly the same thing: taxpayers' money for highly partisan political attacks recently."
Rae countered that his letters did not indulge in "full-throated attacks on an individual" like the Conservative flyers on Trudeau. Rather, he criticized the NDP's stance that a bare majority of 50 per cent plus one vote would be sufficient to trigger negotiations on Quebec secession.
"I don't think there's any comparison in terms of the content. Neither one was in any way, shape or form a personal attack," he said, adding that "nobody should be afraid of political debate."
Mulcair said the NDP has complained to Speaker Andrew Scheer about Rae's letters, seeking clarification about the rules governing the use of "this type of sharp, highly partisan political attack" by MPs.
In fact, NDP whip Nycole Turmel has written Scheer asking for clarification of the rules governing communications sent outside an MP's riding. She has not asked for any clarification on the content of such missives.
— With files from Sue Bailey in Labrador, and Stephanie Levitz in Ottawa.
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