The Board of Supervisors is expected to introduce a bag ban at its meeting tonight.
It would only apply to unincorporated areas in San Mateo County.
However, the move could spur as many as 18 Peninsula cities to launch their own bans.
Shoppers at grocery stores would have to either bring their own bags or pay 10 cents for each paper bag.
San Jose and San Francisco already have similar bans in place.
