OTTAWA - The Conservative Party of Canada is threatening legal action against the Liberals over language they've used to describe an investigation into Tory spending practices.

Lawyers fired off a letter to the president and executive director of the Liberal party, saying a number of Tory staffers have been defamed in a recent opposition press release on the so-called "in and out'' scheme being examined by Elections Canada.

The electoral watchdog is investigating whether several dozen Tory candidates and their official agents improperly claimed local advertising expenses during the last campaign for ads that were national in nature. The Liberals have hammered the Conservatives on the issue daily since Parliament returned this fall.

"This letter is . . . intended to serve as notice that it is defamatory to suggest or imply that these individuals have engaged in illegal conduct,'' writes party lawyer Paul Lepsoe. "In particular, it is defamatory to suggest or imply that the positions these individuals have or have had on Ministers' staffs are 'rewards' for having engaged in illegal conduct.

"Our clients reserve their rights to take such action as they deem appropriate against the Liberal Party of Canada and others . . . .''

The Liberal release, attributed to MP Dominic LeBlanc on Tuesday, refers to an "apparent scheme to violate election spending limits'' and "serious allegations.'' It also underlined that 11 former candidates and agents went on to find government positions.

"One has to wonder if there is a connection between their willingness to participate and employment by this Conservative government,'' LeBlanc said in the statement.

LeBlanc said Thursday he has never said that anybody broke the law.

"What we have said is that Elections Canada has found that 66 Conservative filings did not, in their view, respect the election legislation,'' LeBlanc told reporters. "That's why they have begun an investigation and rejected a series of refunds that the candidates have claimed.''

The Conservative Party is pursuing the Chief Electoral Officer in court for failing to reimburse dozens of its candidate for the advertising expenses.

Prior to that, Elections Canada had begun digging into the details of those claims for more than a million dollars worth of expenses. The Commissioner of Canada Elections is now leading an official investigation.

In documents filed at the Federal Court, Elections Canada said it had found that the Conservative party transferred substantial sums into the bank accounts of candidates across the country -- a practice that is completely legal.

But the candidates immediately sent the money back to the party's head office to pay for television and radio advertisements, expenses the candidates later claimed in order to receive government reimbursements.

The ads were identical to national television and radio spots, except for print in the final frame that either listed ridings or the names of candidates. Some former candidates told Elections Canada and the media that they had no knowledge of what the money was being used for, or that they understood it was to help fund national advertising rather than local expenses.

Government House Leader Peter Van Loan repeated again Thursday during Question Period that his party has acted in accordance with the law.