The Champlain Bridge is Canada's busiest bridge. (Canadian Press)

A Montreal-area coalition is ramping up public pressure for a new Champlain Bridge, to replace the aging structure that connects the island to its South Shore.

A network of mayors, business leaders and interest groups launched an online petition Thursday to bolster their cause, which they say is urgent and of national concern.

The coalition's petition went live less than a day after Liberal Leader Michael Ignatieff promised South Shore voters a new bridge, if he forms the next government in Ottawa.

Members of the coalition say campaign promises are welcome — but what the region needs is swift action.

"The urgency to act is connected to businesses that depend directly on the Champlain Bridge. Especially distribution centres on either side of the river and the trucking industry," said coalition president Martin Fortier, at the petition launch. "The Champlain Bridge is our region's economic lung."

Ignatieff told supporters at a Wednesday night rally that the time has come for a new bridge. "We have to have a new bridge well before 10 years."

The fate of Quebec's aging Champlain Bridge has become a central campaign issue in the Montérégie region south of Montreal.

A local coalition led by Brossard mayor Paul Leduc claims the bridge is a leading issue for suburban voters south of Montreal.

Quebec Premier Jean Charest has named the bridge issue as one of his top federal election wishes.

Numerous reports warn the bridge is on its last legs, and must be replaced – or undergo major repairs – within 10 years.

Earlier this spring, the Conservative government said it would spend $158 million on bridge repairs, but isn’t ready to replace it.

The bridge is Canada’s busiest span, accommodating 60-million cars annually since it was built in 1962.