Former Liberal prime minister Jean Chretien is about to enter the federal election campaign in a big way to attack Thomas Mulcair and the NDP on their plan to repeal the Clarity Act.

At a rally in Hamilton Sunday, Canada’s 20th prime minister will take to the podium to defend what he views as Mulcair’s attack on a united Canada.

What many Canadians fail to realize – and what Chretien knows all too well – is that an NDP government would ignite a new national unity battle in Quebec.

Mulcair has never committed to what terms he would accept if there is another Quebec referendum to separate from Canada.

But he has made a commitment to abolish the Clarity Act.

That alone would create uncertainty about the future of a united Canada.

The Clarity Act sets out the conditions under which the government of Canada would negotiate with a province if it voted for secession.

The Chretien government created it in the spring of 2000 and passed it into law to avoid ambiguity in future referendum questions.

We often forget how close Canada came to separation 20 years ago. Close isn’t the right word – we were on the razor’s edge.

Chretien has spent his life fighting to keep Quebec and Canada together.

He recognizes the threat on the horizon, with Mulcair saying he would abolish the Clarity Act and with the Parti Quebecois once again beating the war drums of separation.

For Chretien, now is the time to act.

Quebec separation would pose the single biggest economic threat to our standard of living as Canadians.

Born and raised in Quebec, Chretien has spent his lifetime fighting the Quebec sovereignty movement.

Given the plans of a Mulcair-led NDP government to do away with the legislation he feels he must do everything possible to protect a united Canada.

Chretien won three majority governments in 1993, 1997 and 2000.

He also served as a cabinet minister in Pierre Trudeau’s and John Turner’s Liberal governments.

One of my best memories of my former political life involves my old boss, the late Dominic Agostino, the former Liberal Member of Provincial Parliament for Hamilton East.

It was October 27, 1995 and we drove to Quebec to attend the Unity Rally in downtown Montreal.

Canada was on the brink of separation and those of us who wanted Canada to stay together were losing the campaign.

Dominic had a passion for a united Canada and for public service.

He said we had to do something -- so we made the trip to Montreal to rally and march for a united Canada.

In the heart of the rally, at the start of the speeches, he told me to get up on his shoulders and look around to see how many people had come to Place du Canada.

There were people for as far as I could see.

All four directions filled with Canada flags and Canadians rallying for a united Canada, just like us.

It was an unbelievable moment to see over 100,000 fellow Canadians attend the biggest political rally in Canadian history, to support their country.

It made me realize that if you really believe in something you need to step up and do something about it.

Chretien was the key speaker at that event and led the way to keep our country to together.

I’ve always believed that rally helped turn the tide to keep Canada together, though I know many others disagree.

Now, at age 81, Chretien the old but fit Liberal warhorse, will step back into the spotlight and make another impact on the future of Canada, and possibly on the Oct. 19 election.

-- Warren is a Liberal political strategist and media commentator. He worked for mayor Mel Lastman and premier Dalton McGuinty and is currently a principal at grgadvisors.ca and CEO of Riseley Gaming Inc.