The statement of claim, which was filed in Ontario Superior Court earlier this month, seeks $3 million for general and special damages for defamation and $1 million in punitive, aggravated and exemplary damages.
The lawsuit names the Canadian Office and Professional Employees Union Local 343 and its strike co-ordinator, Mary Stalteri, as defendants.
According to court documents, Porter alleges libellous comments against the airline were made by Stalteri on behalf of the union through a Twitter account under the username @PorterStrike, which had more than 200 followers as of Wednesday afternoon.
The airline alleges that it was defamed by a video depicting a fake crash with a Porter plane, a fake advertisement and "numerous" comments it says were broadcast from the Twitter account between Jan. 17 through to April 8.
Porter says the tweets used false and misleading information about safety protocols and training practices for the airline and its workers.
"The defamatory statements have caused Porter to suffer significant and unjustifiable damages to its reputation and business, for which the defendants are liable," the airline wrote in the statement of claim.
"The defamatory statements were malicious. The defendants repeatedly, publicly and for no legitimate purpose chose to make statements they knew or should have known to be false. In doing so, the defendants were motivated by a desire to improperly gain leverage in the labour dispute."
Airline spokesman Brad Cicero said Porter had asked the union to "recant" the statements before filing the lawsuit.
"Essentially, we wanted to really make sure that after several warnings that they understand the seriousness of this," he said.
The statement of claim contains allegations that have not been proven in court
Glenn Wheeler, a lawyer for COPE, said it plans on filing a response to the claim in court in the upcoming days.
"Generally, we say that the comments were made in fair comment, in the context of a labour dispute and we will be defending the comments on that basis," he said Wednesday.
Meanwhile, 22 employees who refuel planes for Porter Airlines are still off the job after walking out on Jan. 10.
Talks with a mediator regarding a first contract for the workers, who organized last August, were held last week, but broke down over the issues of wages.
The union says the two sides also cannot agree about benefits and safety.
Porter Aviation Holdings Inc., who employs the workers, has previously said negotiations stalled when the union turned down an average wage increase of 6.1 per cent for this year. Management said the union is asking for a further 5 per cent.
In the interim, Porter has trained replacement workers to fill in during the labour disruption.
Last week, the Toronto Port Authority won a court injunction prohibiting the striking workers from interfering with operations at the island airport, which it owns.
"It is regrettable that the strike has gone on so long, but Porter remains committed to negotiating a fair agreement," said Cicero.
Porter flies to about a dozen cities in Eastern Canada and the United States and carried 2.45 million passengers last year.
Last week, the airline announced plans to seek permission to fly jets out its main base on Toronto's waterfront after placing a conditional order for 12 Bombardier CS100 aircraft, with options for 18 more.
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