RCMP searched Conservative party headquarters in Ottawa on Tuesday at the request of Elections Canada.
Elections Canada spokesman John Enright confirmed that elections commissioner William Corbett requested the assistance of the Mounties to execute a search warrant, but he wouldn't say why.
Conservative House Leader Peter Van Loan later said during question period the search was "in relation to the issue of the campaign financing questions and our approach on spending."
Camera crews, including one from the Liberal party, were on hand as police arrived at the downtown building.
CBC News first reported RCMP officers were seen in the 12th-floor party offices and the 17th-floor mailroom. An elections official later left with a box of documents.
RCMP Cpl. Jean Hainey said the Mounties were merely assisting.
"It is not an RCMP investigation. We're there to assist, but that's it."
Elections Canada is probing Conservative party spending for advertisements during the 2006 parliamentary election campaign. Corbett, who enforces the Elections Canada Act, launched an investigation in April 2007 after chief electoral officer Marc Mayrand challenged the spending claims.
Money sent to local offices
The Conservative Party of Canada, having reached the $18.3-million advertising spending limit set out under the Canada Elections Act, transferred cash to 66 local campaign offices.
The local campaigns sent the money back to national party headquarters to buy local television and radio advertisements for their candidates.
Elections Canada says the advertisements produced through the local offices didn't qualify as local spending because they were too similar to national ads. The ads looked exactly the same as the national ads, except for small print or the names of the individual candidates.
Financial agents for some of the Conservative candidates later asked to be reimbursed for those expenses. Candidates who get 10 per cent of the votes in their riding get a portion of their election expenses returned from Elections Canada.
Elections Canada refused, saying the party paid for the ads, not the candidates.
The Conservatives maintain they didn't break any rules.
Soon after Corbett launched his investigation, the Conservatives went to Federal Court in an attempt to force Mayrand to reimburse the expenses to the Conservative candidates. That case has not yet reached a hearing stage, with the party and Elections Canada still filing evidentiary briefs.
Search dominates question period
Opposition politicians, who have called it an "in-and-out" scheme, grilled the government on the election spending issue during a raucous question period Tuesday.
"What will it take for the prime minister to finally admit that the Conservative Party broke the law?" Liberal Leader Stéphane Dion asked.
Prime Minister Stephen Harper dismissed Dion's charges as "completely false" and said lawyers for his party were preparing to interview Elections Canada officials on Wednesday in their pending lawsuit against the federal body.
"Our legal position is rock-solid," Harper said.
Dion accused of the government of stonewalling an Elections Canada probe into the matter by launching its own lawsuit.
Harper said the party has provided Elections Canada with every document it has requested, adding he doesn't know why it was necessary to call in the RCMP.
NDP Leader Jack Layton said the government has "closed the door on transparency" to Canadians.