Think before you say next time Double Bag It during shopping - for it could cost you more than what you think. If San Francisco's Board of Supervisors have its way, a legislation would soon be enforced that would expand the city's restriction on checkout bags to include all retail stores and restaurants and customers would have to pay for each bag the business establishment provides.

The legislation sponsored by Supervisor Ross Mirkarimi would be put to vote before the Board of Supervisors on Tuesday and if passed, would require shoppers in San Francisco to pay $0.10 per bag provided by the store at the checkout, starting July 1, 2012. And, if you think that's pricey, think again - the charge would jump to $0.25 per bag after 2 years.

The legislation also expands the city's current ban on plastic bags in grocery stores and drug stores to all retail stores, clothing boutiques and bookstores from July 1.

Restaurants will also be banned from allowing takeouts in plastic bags from that day but leftover portions of sit-down meals will be allowed to be taken home in plastic containers.

In other words, starting July 1, expect to see only recyclable paper bags, compostable bags or reusable bags being offered in all retail establishments. Don't expect to see any plastic bags because if a store doesn't comply with the law, the Department of Environment would ensure that it is fined $100 for the first infraction, $200 for the second and $500 each time after that.

However, certain types of plastic bags will still be allowed e.g., plastic wraps for meat and flowers, dry cleaning bags, etc.

Want to save some dimes (or quarters)? Start making the habit of bringing your own bag when you go shopping.

The legislation, which is Mirkarimi's final act before he's sworn in as the new sheriff in January, could help San Francisco's population reduce its usage of plastic bags by 60-80 per cent.

Melanie Nutter, director of the Department of the Environment, said plastic bags are harmful as the choke waterways, clog storm drains and harm wildlife and the original ban had helped reduce the footprint of plastic bags in the city's waste streams by 18 percent.

Plastic bags continue to be a problem in San Francisco, SFGate.com quoted Nutter as saying. More needs to be done, she added. Mirkarimi's legislation could then be the magic potion Nutter is looking for.

However, if the bill passes as expected, 'Save The Plastic Bag Coalition' group is expected to file a lawsuit, saying there has not been enough environmental review.