A union card is “a ticket into middle-class stability,” according to a new study that shows most union members earn incomes that put them at the upper end of the income spectrum in Canada.

As a result, efforts to shore up the country’s disappearing middle class should include measures to support collective bargaining, says the study by the left-leaning Canadian Centre for Policy Alternatives being released Friday to mark International Workers’ Day.

“We can expect the middle class to shrink and upward mobility to stall, as long as union representation continues to decline,” said economist Hugh Mackenzie, co-author of the study with statistician Richard Shillington.

About 45 per cent of full-time workers earning upper-middle-class wages are union members, while just 8 per cent of Canada’s lowest income earners belonged to a union, the study says. (The average upper-middle-class wage for a single person was $78,352, before taxes, in 2011. The lowest income earners made an average of $8,560.)

The study, which looked at union membership between 1997 and 2011, found that the overall percentage of unionized workers has been relatively stable at 27 per cent.

But the loss of unionized jobs in the private sector during this period — from 21 per cent to 14 per cent — resulted in many workers getting “kicked out of the middle class,” Mackenzie said.

Workers who lost unionized jobs during the economic downturn in 2008 saw their incomes drop by about 9 per cent, the report says.

However, workers who joined a union during the recession saw their incomes jump by about 39 per cent.

“The findings suggest that there is a huge opportunity cost for workers who lose a unionized position, especially during recessionary periods,” Mackenzie said.

“Conversely, workers represented by a union tend to move a notch or two up the income ladder,” he said. “They’re not only better positioned to weather economic storms, they’re more likely to experience the Canadian middle-class dream of upward income mobility.”

As politicians battle for the middle-class vote in next fall’s federal election, they can’t ignore the role unions play in bolstering the middle class, he said.

“Any policy discussion around middle-class economics should examine these startling trends and reconsider ways to facilitate the rise of collective bargaining in Canada’s future,” he said. “The health of the middle class depends on it.”