A merger of two of Canada's largest private-sector unions is needed to help combat the federal Conservative government's attack on the labour movement, the head of the Canadian Auto Workers union said Monday.

"What (Prime Minister Stephen) Harper hates is strong commitment to social unionism," Ken Lewenza told a CAW convention in referring to the proposed merger with the Communications, Energy and Paperworkers Union.

Lewenza said federal intervention in negotiations involving CP Rail, Canada Post and Air Canada workers had been an attack workers' rights.

Meanwhile, the government's move to change rules around employment insurance is an attempt to "bully and punish" workers who have lost their jobs, the CAW president said.

His remarks came at the CAW kicked off its constitutional and collective bargaining convention in Toronto with songs and a procession of more than 400 retired autoworkers.

During the convention, members will vote on a proposal to merge with the Communications, Energy and Paperworkers Union of Canada, a move that key players have said would revitalize the labour movement.

The CAW began contract talks with the big U.S. automakers — GM, Ford and Chrysler — last week.

The union, which made concessions on wages, vacation time and other benefits when the U.S. automakers were struggling during the 2008-09 recession, has said it wants to share in the profits now that the industry has rebounded.

The automakers have said their focus during the negotiations will be to improve competitiveness at their Canadian operations, where labour costs are higher than in the United States.