Prime Minister Stephen Harper has defended plans to spend millions of taxpayer dollars on advertising to promote his government's pre-election budget after details of the campaign became public.

Internal documents show Finance Canada is planning a $7.5-million ad campaign that will run in May.

"The campaign will illustrate how the [Economic Action Plan] is on track to positioning Canada for success in the 21st century global economy through a series of measures," states a Public Works document obtained by CTV and viewed by The Globe and Mail that outlines details of the campaign.

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NDP Leader Thomas Mulcair and Liberal Leader Justin Trudeau criticized the plan in the House of Commons, but Mr. Harper stood by the move.

"When we talk about the budget, I can assure the honourable member the government will not only bring forward a budget, but we will make sure Canadians are well aware of the contents of that budget and how those measures impact them," Mr. Harper said in response to a question from Mr. Mulcair.

Using government advertising to promote the budget is nothing new for the Conservatives. Last year, Finance spent $7.5-million on Economic Action Plan ads, and other departments ran similar campaigns. Employment and Social Development spent $7-million on a skills initiative campaign, and the Canada Revenue Agency spent $6-million last year on ads focused on encouraging people to take advantage of new tax measures.

Annual spending on advertising has declined from a high of $136.3-million in 2009-10 during the height of stimulus spending to $69-million in 2012-13.

The annual report with official numbers on advertising spending for the 2013-14 fiscal year has not yet been released.

Finance Minister Joe Oliver is scheduled to make an announcement on Thursday in Toronto, fuelling expectations he will set a date for the budget.

Critics of the federal approach to advertising say Ottawa should follow the lead of the Ontario government, which requires the Auditor-General to approve all advertising to ensure it is not partisan.

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Queen's University political science professor Jonathan Rose, who advises Ontario's Auditor-General on advertising issues, says the proximity of the upcoming ad campaign to the election is a concern.

"What's so egregious is the blatant way that they're priming the electorate before an election, and I think that should be worrisome as well," he said.

Liberal MP David McGuinty, who has put forward a private members bill that would establish independent oversight of federal advertising, said the Conservatives are producing government ads that have the same colours and imagery as the political ads paid for by the Conservative Party.

"In the classic definition of the word, it's propaganda," he said. "It's working for them, or they wouldn't be doing it."

The document produced by Public Works, which is responsible for government advertising, says the campaign will promote measures from the budget and the government's 2014 fall economic update.

"The Department of Finance will continue to implement the umbrella advertising campaign flowing from the EAP, including the Fall Economic Update, which is integral to meeting the Government's number-one priority of growing the Canadian economy and creating jobs while returning to balanced budgets in 2015," the document states.

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Both the NDP and Liberals have written to Mr. Oliver asking the government to cut spending on advertising as a way to save money.