"Reducing the volume of plastic bags that end up in landfills is a top priority for us," she said.

Broten announced a partnership with the Recycling Council of Ontario, grocer and retail associations, as well as a plastics industry group, in order to meet the targets.

The plan would slash the use of plastic bags by 50 percent over five years, and promote recycling and the use of reusable bags for shopping.

"We're going to take a billion bags out of circulation in the next five years. We're going to make sure that retailers right across the province have other options available," Broten told a news conference. "At the same time, we're going to put in various incentive programs."

If the voluntary system doesn't work, Ontario may consider tougher measures such as plastic-bag fees or outright bans.

The plan won only a tepid response from environmentalists.

"We think that the province is going down the slow road to waste reduction," said Lina Cino of the Toronto Environmental Alliance. "We think that the voluntary program doesn't give any reassurance to the public that something is actually going to get done."

Cino suggested Ontario should follow the lead of San Francisco, which announced earlier this year it would phase in a ban on non-biodegradable plastic bags after a voluntary program didn't work.

Countries like Ireland have also taken a firm stance on the issue, charging for use of grocery bags, added Cino.