THE BAN THE BAG RALLY at city hall on Wednesday, July 14, went down exactly how you would expect. There were impassioned environmentalist talking points. There was a drum circle.

But a surprise came two days later: The Northwest Grocery Association (NWGA), which represents the big grocery stores who will be affected by the proposed citywide ban on plastic bags, came out in support of the green groups' plan. How did big business get on the side of the hippies?

The answer, of course, lies in dollars and cents. Though they only cost about a penny to buy, plastic bags rack up costs for businesses.

The resolution Mayor Sam Adams' office pitched last week with the backing of the Surfrider Foundation and Environment Oregon will ban large Portland grocery stores from handing out plastic bags at the checkout stand and charge shoppers five cents for each paper bag. City council will likely vote on the plan in August but the rules would not go into effect until 2012, giving the legislature time to pass a statewide ban on the bags that make up 12 percent of ocean litter.

NWGA President Joe Gilliam explains that the idea that shoppers are handed a free bag in the checkout line is a myth.

"They're a cost of business that shows up in the price of milk and eggs," says Gilliam.

Gilliam's group has worked with politicians and environmentalists for three years to craft Portland's ban. Seattle learned the hard way what happens when cities try to ban the bag without strong business support: Seattle voters repealed their city's 20-cent bag tax in 2009.

"We're better off when more people bring in reusable bags, because we're able to lower our costs," says Gilliam, adding that paper bags cost groceries six to eight cents each. "We're aware that we're asking Oregonians to make a big behavioral change."

The American Chemistry Council, which represents plastic bag manufacturers and poured $1.5 million into fighting Seattle's bag tax, says cities should focus on promoting plastic bag recycling rather than banning the bags outright.

But Jeff Murray, vice president of business development for major local recycler Far West Fibers, would rather plastic bags disappear altogether. When the bags are mixed in with curbside recycling, they get caught in Far West Fibers' sorting machine, gumming up the works so severely that crews have to stop the machine and clean it out four times a day. That adds up to a labor cost of $60,000 a year.

National recycler SP Recycling reports a similar shocking cost. Though plastic bags make up only .1 percent of their intake, they consume 20-30 percent of labor costs.

Both Gilliam and Murray have the same comment on Mayor Adams' bag ban plan: It doesn't go far enough. To keep competition fair, they want a plastic ban plus five-cent paper bag fee at all grocery stores statewide.