Del Mastro, who now sits in the House of Commons as an Independent, entered the plea today in provincial court in Peterborough, Ont.
Richard McCarthy, Del Mastro's official agent for the campaign, was not present during the arraignment hearing, but his lawyer, David McFadden, entered the plea on his behalf.
A trial that could last two weeks or more is scheduled to begin June 23.
The commissioner of Canada elections has accused Del Mastro of overspending during the 2008 federal election campaign.
He is also charged with failing to report a personal contribution of $21,000 to his own campaign, far in excess of the personal contributions limit of $2,100. Del Mastro, meanwhile, has insisted he did nothing wrong.
Elections Canada also alleges that Del Mastro tried to cover up his overspending by knowingly submitting a falsified document.
McCarthy also faces three charges, including "incurring election expenses in an amount more than the election expenses limit."
Outside the courthouse, Del Mastro said he is looking forward to clearing his name and representing the constituents of his Peterborough riding.
His lawyer, Jeffrey Ayotte, said he, McFadden and the Crown have agreed to a statement of facts and a book of documents to be filed with the court to expedite the proceedings next month.
A nearly two-year investigation into Del Mastro's 2008 election campaign focused on the $21,000 payment he made to a consulting firm from his personal account, which did not appear on his official campaign return and which would have put him over the campaign spending limit.
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