The Alberta NDP Leader Brian Mason sent a letter to four party leaders on Friday expressing concern over the tone of the campaign.

The letter, sent to PC Leader Alison Redford, Liberal Leader Raj Sherman, Wildrose Leader Danielle Smith and Alberta Party Leader Glenn Taylor, expressed apprehension over how the campaign has unfolded.

"I’m concerned about the negative personal tone that has developed in the first five days of this campaign," Mason wrote.

Mason mentioned that in the past week one leader’s loyalties to Alberta have been questioned, referring to Smith's accusation that Redford did not like Alberta. Another leader (Sherman) showed up at another leader's public event (Redford), and parties have resorted to using "aggressive" robocalls and push-polling, Mason said.

"The issues are what are important – not personal attack," he wrote. "We now have only 23 days left to share our ideas with millions of Albertans."

He urged the other leaders to focus on the discussion of issues that matter and make a difference to "everyday Albertans."

"Let’s have a vigorous, but fair debate this election."