Ken Lewenza, the head of the Canadian Autoworkers Union, and Dave Coles, the president of the Communications, Energy and Paperworkers Union of Canada, have announced they are resigning.
The two men made the announcement at a news conference in Toronto on Thursday.
The two unions voted last year to merge and the leaders endorsed senior CAW official Jerry Dias to be the first president of the new combined union, to be called Unifor.
Lewenza said his last day will be Oct. 1, 2013. "I'll be an ambassador for Unifor, I'll be an activist," Lewenza said of his post-retirement plans.
Dias, a top lieutenant under Lewenza's tenure at the top, has worked his way up the CAW ranks during the last 35 years.
Lewenza said, at 59 years old, he wasn't willing to commit to the work that needs to be done as Unifor merges and expands from its base. "This is not a one-year job, this is a three- or four-year job, minimum," for whoever heads up the new union.
Lewenza was elected the national president of the CAW in 2008, replacing Buzz Hargrove, and Coles has been president of the CEP since 2006.
"Kenny’s very dynamic and a great leader," Hargrove said of his successor. "The thing Kenny always cared about is what he leaves behind.
"He obviously came to the conclusion it was in the best interest of the union," Hargrove said Thursday.
The new union will represent more than 300,000 workers across roughly 20 sectors of the economy, primarily in manufacturing, communications and transportation. Unifor will be the country's biggest private sector union.
During an earlier interview with CBC News, when he was working on merger plans, Lewenza indicated that leading a union is getting tougher.
"We got the privilege of representing the workers, they got the privilege of putting us in putting us out," Lewenza said. "But at the end of the day, man, it's a bigger job today than it was 40 years ago."
Unifor will also represent some public sector employees in the health, education and transit sectors.