With the government expected to fall Friday, the tone of the political cut and thrust has already gotten nasty with attack ads airing even before the campaign gets underway.

And one political observer says it's only going to get worse when Prime Minister Stephen Harper drops the election writ, as he is widely expected to do this weekend.

Bernard Gauthier, head of the Ottawa public relations firm Delta Media, says attack ads run the risk of alienating voters if they are perceived as "hitting below the belt," but adds that appears to be a risk the major political parties are prepared to take.

"What's interesting is that when you start off in an election campaign you never know where that line is: where that belt is that you can't hit below," Gauthier told CTV's Canada AM.

"Generally the parties feel around until all of a sudden they hit there, the public and the news media react and they typically withdraw the ad right away and say: ‘No, no, it was a misunderstanding or a mistake.'

"And it can definitely hurt them in the polls because it starts to call into question the fairness of the party and Canadians do have a sense of fairness when it comes to elections."

Perhaps the most famous example of a Canadian political ad backfiring was the Tory television campaign during the 1993 election campaign that appeared to mock Liberal Leader Jean Chretien's facial defigurement, the result of a childhood disease.

"That was one of the first and most important examples of an attack ad that hit below the belt," Gauthier said. "Immediately people sensed that this was way below the belt and it certainly didn't help (Conservative leader) Kim Campbell's chances."

Although the Tories quickly withdrew the offending ad, they went down to the worst election defeat in Canadian history falling from a majority government to only two seats in the House of Commons.

In the last federal election campaign, the Liberals made a misstep with ads that attempted to frighten voters away from electing Stephen Harper, warning ominously that his policies would result in "Soldiers with guns in our cities. In Canada."

That campaign flopped because it took Tory policy too far out of context.

In the current, pre-election campaign, both the Conservatives and the Liberals seem to be trying to walk the fine line between attacking their opponents and taking personal pot-shots.

For the past few weeks, the Conservatives have been airing a series of television ads questioning Liberal Leader Michael Ignatieff's commitment to Canada, warning voters: "He's not in it for you or for Canada. He's just in it for himself. It's the only reason he's back. Michael Ignatieff. Just visiting"

The Liberals fired back with their own attack on Harper, listing government scandals and concluding: "Harper thinks he's above the law. Is this your Canada? Or Harper's?"

Gauthier said that already combative tone won't improve once the election is finally called.

"The ads that I've seen so far don't augur well for the upcoming election … we've really moved now to ads that attack people personally," he said.

With the Internet, social media sites and blogs playing a bigger role in political campaigns, he says there is more and more opportunity for all political parties to fly trial balloons -- attack ads that push the boundaries of what is acceptable in a Canadian election campaign.

"That's a new feature of elections now, things that are posted on websites or posted on blogs," he said. "All of that now comes into play, so it's a lot more complex landscape because the messages appear in more places.

The deciding factor for Gauthier is what kind of images the ads use of their target, usually the leader of the opposing parties. "That for me is the mark of attack ads: that the visual is primarily a very negative, detrimental photo of the other party's leader."